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Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	Dec. 31, 2018	Feb. 15, 2019	Jun. 29, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Trading Symbol	TNDM
Entity Registrant Name	TANDEM DIABETES CARE INC
Entity Central Index Key	0001438133
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		57,717,618
Entity Public Float			$ 1.1

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 41,826	$ 13,700
Short-term investments	87,201	479
Accounts receivable, net	35,193	20,793
Inventory, net	19,896	26,993
Prepaid and other current assets	3,769	2,191
Total current assets	187,885	64,156
Property and equipment, net	17,151	19,631
Restricted cash - long-term		10,000
Other long-term assets	128	102
Total assets	206,294	95,346
Current liabilities:
Accounts payable	6,824	5,150
Accrued expense	3,930	2,832
Employee-related liabilities	24,030	14,488
Deferred revenue	4,600	2,526
Common stock warrants	17,926	5,432
Other current liabilities	8,978	5,657
Total current liabilities	66,288	36,085
Notes payable—long-term		76,541
Deferred rent—long-term	3,799	4,687
Other long-term liabilities	4,932	7,181
Total liabilities	75,019	124,494
Commitments and contingencies
Stockholders’ equity (deficit):
Common stock, $0.001 par value; 200,000 and 100,000 shares authorized as of December 31, 2018 and December 31, 2017, respectively. 57,554 and 10,119 shares issued and outstanding at December 31, 2018 and December 31, 2017, respectively.	57	10
Additional paid-in capital	731,306	448,455
Accumulated other comprehensive loss	(13)
Accumulated deficit	(600,075)	(477,613)
Total stockholders’ equity (deficit)	131,275	(29,148)
Total liabilities and stockholders’ equity (deficit)	206,294	95,346
Patents [Member]
Current assets:
Patents, net	$ 1,130	$ 1,457

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	100,000,000
Common stock, shares issued	57,554,000	10,119,000
Common stock, shares outstanding	57,554,000	10,119,000

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Sales	$ 183,866	$ 107,601	$ 84,248
Cost of sales	94,044	63,507	60,656
Gross profit	89,822	44,094	23,592
Operating expenses:
Selling, general and administrative	105,226	86,377	82,834
Research and development	29,227	20,661	18,809
Total operating expenses	134,453	107,038	101,643
Operating loss	(44,631)	(62,944)	(78,051)
Other income (expense), net
Interest and other income	1,462	239	296
Interest and other expense	(7,584)	(11,341)	(5,707)
Loss on extinguishment of debt	(5,313)
Change in fair value of stock warrants	(66,494)	1,021
Total other expense, net	(77,929)	(10,081)	(5,411)
Loss before taxes	(122,560)	(73,025)	(83,462)
Provision for income tax (benefit) expense	51	8	(15)
Net loss	(122,611)	(73,033)	(83,447)
Other comprehensive loss:
Unrealized gain (loss) on short-term investments	(13)	1	(21)
Comprehensive loss	$ (122,624)	$ (73,032)	$ (83,468)
Net loss per share - basic and diluted	$ (2.55)	$ (12.87)	$ (27.30)
Weighted average shares used to compute basic and diluted net loss per share	48,129	5,677	3,057

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2015	$ 63,468	$ 3	$ 384,578	$ 20	$ (321,133)
Balance, Shares at Dec. 31, 2015		3,026,000
Exercise of stock options	170		170
Exercise of stock options, Shares		15,000
Issuance of common stock for Employee Stock Purchase Plan	2,151		2,151
Issuance of common stock for Employee Stock Purchase Plan, Shares		69,000
Stock-based compensation	11,752		11,752
Unrealized gain (loss) on short-term investments	(21)			(21)
Net loss	(83,447)				(83,447)
Balance at Dec. 31, 2016	(5,927)	$ 3	398,651	(1)	(404,580)
Balance, Shares at Dec. 31, 2016		3,110,000
Exercise of stock options	$ 270		270
Exercise of stock options, Shares	24,406	24,000
Issuance of common stock in public offering, net of underwriter’s discount and offering costs	$ 33,353	$ 7	33,346
Issuance of common stock in public offering, net of underwriter’s discount and offering costs, Shares		6,946,000
Issuance of common stock warrants in connection with term loan	3,331		3,331
Issuance of common stock for Employee Stock Purchase Plan	300		300
Issuance of common stock for Employee Stock Purchase Plan, Shares		39,000
Stock-based compensation	12,557		12,557
Unrealized gain (loss) on short-term investments	1			1
Net loss	(73,033)				(73,033)
Balance at Dec. 31, 2017	(29,148)	$ 10	448,455		(477,613)
Balance, Shares at Dec. 31, 2017		10,119,000
Exercise of stock options	$ 1,027		1,027
Exercise of stock options, Shares	136,042	136,000
Exercise of common stock warrants	$ 29,575	$ 9	29,566
Exercise of common stock warrants, Shares		8,603,000
Issuance of common stock in public offering, net of underwriter’s discount and offering costs	172,929	$ 39	172,890
Issuance of common stock in public offering, net of underwriter’s discount and offering costs, Shares		38,535,000
Fair value of common stock warrants at time of exercise	54,000		54,000
Issuance of common stock for Employee Stock Purchase Plan	1,364		1,364
Issuance of common stock for Employee Stock Purchase Plan, Shares		81,000
Stock-based compensation	24,003		24,003
Stock-based compensation, Shares		80,000
Unrealized gain (loss) on short-term investments	(13)			(13)
Adjustment to retained earnings from adoption of ASC 606	149				149
Net loss	(122,611)				(122,611)
Balance at Dec. 31, 2018	$ 131,275	$ 57	$ 731,306	$ (13)	$ (600,075)
Balance, Shares at Dec. 31, 2018		57,554,000

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended			27 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017
Operating activities
Net loss	$ (122,611)	$ (73,033)	$ (83,447)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	5,821	6,866	5,489
Interest expense related to amortization of debt discount and debt issuance costs	1,721	1,883	274
Payment in kind interest accrual of notes payable		1,657	927	$ 2,700
Provision for allowance for doubtful accounts	1,448	824	632
Provision for inventory reserve	607	26	3,343
Change in fair value of common stock warrants	66,494	(1,021)
Amortization of premium (discount) on short-term investments	539	(16)	(85)
Stock-based compensation expense	23,736	12,628	11,660
Loss on extinguishment of debt	5,313
Other	152	159	(78)
Changes in operating assets and liabilities:
Accounts receivable, net	(15,848)	(10,445)	2,251
Inventory, net	6,756	(5,894)	(6,904)
Prepaid and other current assets	(1,576)	1,831	(2,466)
Other long-term assets	(26)	4	(2)
Accounts payable	1,641	(1,953)	3,234
Accrued expense	1,097	1,203	(497)
Employee-related liabilities	9,542	3,873	(1,578)
Deferred revenue	2,074	(3,906)	4,610
Other current liabilities	3,219	260	573
Deferred rent	(785)	(692)	1
Other long-term liabilities	2,367	(390)	890
Net cash used in operating activities	(8,319)	(66,136)	(61,173)
Investing activities
Purchases of short-term investments	(123,553)		(30,622)
Proceeds from sales and maturities of short-term investments	35,800	8,500	50,000
Purchase of property and equipment	(2,986)	(5,718)	(8,930)
Net cash provided by (used in) investing activities	(90,739)	2,782	10,448
Financing activities
Issuance of notes payable, net of issuance costs			49,994
Principal payments on notes payable	(87,711)
Proceeds from public offering, net of offering costs	172,929	39,806
Proceeds from issuance of common stock under Company stock plans	2,391	570	2,321
Proceeds from exercise of common stock warrants	29,575
Net cash provided by financing activities	117,184	40,376	52,315
Net increase (decrease) in cash and cash equivalents and restricted cash	18,126	(22,978)	1,590
Cash and cash equivalents and restricted cash at beginning of period	23,700	46,678	45,088
Cash and cash equivalents and restricted cash at end of period	41,826	23,700	46,678	$ 23,700
Supplemental disclosures of cash flow information
Interest paid	10,805	7,876	4,401
Income taxes paid	16	22	23
Supplemental schedule of noncash investing and financing activities
Lease incentive - lessor-paid tenant improvements	13	3,292
Property and equipment included in accounts payable & other current liabilities	125	92	501
Debt discount included in other long-term liabilities		4,137	$ 1,509
Common stock warrants issued in connection with term loan		$ 3,331
Unsettled purchase of investments classified as cash equivalents in other current liabilities	$ 1,708

Organization and Basis of Presentation

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Basis of Presentation

1. Organization and Basis of Presentation

The Company

Tandem Diabetes Care, Inc. is a medical device company focused on the design, development and commercialization of products for people with insulin-dependent diabetes. The Company is incorporated in the state of Delaware. Unless the context requires otherwise, the terms the “Company” or “Tandem” refer to Tandem Diabetes Care, Inc.

The Company manufactures and sells insulin pump products that are designed to address large and differentiated needs of the insulin-dependent diabetes market. The Company’s manufacturing and sales activities primarily focus on the t:slim X2 Insulin Delivery System, or t:slim X2, the Company’s flagship pump platform that is capable of remote feature updates and designed to display continuous glucose monitoring, or CGM, sensor information directly on the pump home screen. The Company’s insulin pump products are generally considered durable medical equipment, and have an expected lifespan of at least four years. In addition to selling insulin pumps, the Company sells disposable products that are used together with the pumps and are replaced every few days, including cartridges for storing and delivering insulin, and infusion sets that connect the insulin pump to a user’s body. The Company’s insulin pump products are compatible with the Tandem Device Updater, a Macand PC-compatible tool for the remote update of Tandem insulin pump software.

The Company began commercial sales of its first product, t:slim, in August 2012 and subsequently commercialized t:flex in May 2015, t:slim G4 in September 2015 and t:slim X2 in October 2016. The t:slim X2 hardware platform now represents 100% of new pump shipments, but the Company will continue to provide ongoing service and support to existing t:slim, t:slim G4 and t:flex customers. In June 2018, the Company received approval by the United States Food and Drug Administration, or FDA, for t:slim X2 with Basal-IQ technology, the Company’s first-generation Automated Insulin Delivery, or AID, algorithm, and commenced commercial sales of this product in August 2018.

During the third quarter of 2018, the Company commenced sales of the t:slim X2 in select geographies outside the United States, including Australia, Italy, New Zealand, Scandinavia (Denmark, Norway and Sweden), South Africa, Spain, and the United Kingdom.

The consolidated financial statements included in this Annual Report have been prepared on a basis that assumes that the Company will continue as a going concern, and do not include any adjustments that may result from the outcome of this uncertainty. This basis of accounting contemplates the recovery of the Company’s assets and the satisfaction of the Company’s liabilities and commitments in the normal course of business and does not include any adjustments to reflect the possible future effects of the recoverability and classification of recorded asset amounts or amounts and classification of liabilities that might be necessary should the Company be unable to continue as a going concern.

At December 31, 2018, the Company had $129.0 million in cash and cash equivalents and short-term investments. The Company has incurred operating losses since its inception and, as reflected in the accompanying consolidated financial statements, the Company had an accumulated deficit of $600.1 million as of December 31, 2018. Management believes that cash and cash equivalents and short-term investments on hand will be sufficient to satisfy the Company’s liquidity requirements for at least the next 12 months from the date of this filing.

The Company’s ability to execute on its business strategy, meet its future liquidity requirements, and achieve and maintain profitable operations, is dependent on a number of factors, including its ability to continue to gain market acceptance of its products and achieve a level of revenues adequate to support its cost structure, achieve renewal pump sales objectives, develop and launch new products, increase gross profits from higher sales of infusion sets, maximize manufacturing efficiencies, satisfy increasing production requirements, leverage the investments made in its sales, clinical, marketing and customer support organizations and operate its business and manufacture and sell products without infringing third party intellectual property rights.

The Company has funded its operations primarily through private and public equity and debt financing. The Company may in the future seek additional capital from public or private offerings of its capital stock, or it may elect to borrow additional amounts under new credit lines or from other sources. If the Company issues equity or debt securities to raise additional funds, its existing stockholders may experience dilution, it may incur significant financing costs, and the new equity or debt securities may have rights, preferences and privileges senior to those of its existing stockholders. There can be no assurance that equity or debt financing will be available on acceptable terms, or at all.

Basis of Presentation and Principles of Consolidation

The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America, or GAAP, and include the accounts of Tandem Diabetes Care, Inc. and its wholly owned subsidiary in Canada. All significant intercompany balances and transactions have been eliminated in consolidation.

Reverse Stock Split

On October 9, 2017, the Company effected a 1-for-10 reverse stock split of its issued and outstanding shares of common stock. The par value per share and the authorized number of shares of common stock and preferred stock were not adjusted as a result of the reverse stock split. All common stock share and per-share amounts for all periods presented in these consolidated financial statements have been adjusted to reflect the reverse stock split.

Reclassifications

Certain reclassifications of prior year amounts related to the presentation of restricted cash on the statement of cash flows have been made to conform to the current year presentation.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Use of Estimates

The preparation of the consolidated financial statements in conformity with GAAP requires management to make informed estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, and the disclosure of contingent assets and liabilities in the Company’s consolidated financial statements and accompanying notes as of the date of the consolidated financial statements. Actual results could differ materially from those estimates and assumptions.

Segment Reporting

Operating segments are identified as components of an enterprise about which discrete financial information is available for evaluation by the chief operating decision-maker, or the CODM in making decisions regarding resource allocation and assessing performance. The Company’s current product offering consists primarily of insulin pumps, disposable cartridges and infusion sets for the storage and delivery of insulin. The Company has viewed its operations and managed its business as one segment as key operating decisions and resource allocations are made by the CODM using consolidated financial data.

Cash Equivalents

The Company considers all highly liquid investments with a maturity of three months or less from the date of purchase and that can be liquidated without prior notice or penalty, to be cash equivalents.

Short-Term Investments

Based on the nature of the assets, the Company’s short-term investments are classified as either available-for-sale or trading securities. Such securities are carried at fair value as determined by prices for identical or similar securities at the balance sheet date. The Company’s short-term investments consist of Level 1 and Level 2 financial instruments in the fair value hierarchy. The net unrealized gains or losses on available-for-sale securities are reported as a component of other comprehensive loss within the statements of operations and accumulated other comprehensive loss as a separate component of stockholders’ equity (deficit) on the consolidated balance sheets. Unrealized gains or losses on trading securities are reported as a component of other income or expense within the consolidated statements of operations. The Company determines the realized gains or losses of available-for-sale securities using the specific identification method and includes net realized gains and losses as a component of other income or expense within the consolidated statements of operations. The Company periodically reviews available-for-sale securities for other than temporary declines in fair value below the cost basis whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. To date, the Company has not identified any other than temporary declines in fair value of its short-term investments.

Restricted Cash

The Company recorded $10.0 million of restricted cash as of December 31, 2017, for the minimum cash balance requirement in connection with the Term Loan Agreement (see Note 5, Term Loan Agreement). Due to the full repayment of the term loan in August 2018, no restricted cash balance was required at December 31, 2018.

In January 2018, the Company adopted new guidance from the Financial Accounting Standards Board or the FASB that clarified how entities should classify certain cash receipts and cash payments on the statement of cash flows. As a result, the restricted cash balance that existed in prior periods is included as a component of cash and cash equivalents and restricted cash on the statement of cash flows in the relevant periods presented.

Accounts Receivable

The Company grants credit to various customers in the ordinary course of business. The Company maintains an allowance for doubtful accounts for potential credit losses. Provisions are made based on historical experience, assessment of specific risk, review of outstanding invoices, and various assumptions and estimates that are believed to be reasonable under the circumstances. Uncollectible accounts are written off against the allowance after appropriate collection efforts have been exhausted and when it is deemed that a balance is uncollectible.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash, cash equivalents, short-term investments and accounts receivable. The Company maintains deposit accounts in federally insured financial institutions in excess of federally insured limits. The Company also maintains investments in money market funds that are not federally insured. Additionally, the Company has established guidelines regarding investment instruments and their maturities, which are designed to maintain preservation of principal and liquidity.

The following table summarizes customers who accounted for 10% or more of net accounts receivable:

	December 31,
	2018			2017
Byram Healthcare		15.5	%		17.2	%
CCS Medical, Inc.		10.1	%		16.2	%
Edgepark Medical Supplies, Inc.	N/A				17.7	%

The following table summarizes customers who accounted for 10% or more of sales for the periods presented:

	Year Ended December 31,
	2018			2017			2016
Edgepark Medical Supplies, Inc.		19.4	%		21.5	%		18.7	%
Byram Healthcare		15.6	%		14.0	%		14.0	%
Solara Medical Supplies, Inc.	N/A			N/A				10.7	%
CCS Medical	N/A				10.3	%	N/A

Fair Value of Financial Instruments

The carrying amounts of cash and cash equivalents, accounts receivable, accounts payable, accrued expense, and employee-related liabilities are reasonable estimates of their fair values because of the short-term nature of these assets and liabilities. Short-term investments are carried at fair value. The Company believes the fair value of its long-term notes payable at December 31, 2017 approximated its carrying value, based on the borrowing rates that were available for loans with similar terms. The estimated fair value of certain of the Company’s common stock warrants was determined using the Black-Scholes pricing model as of December 31, 2018 and 2017, as discussed in Note 4.

Certain trade-in rights previously offered by the Company pursuant to the Technology Upgrade Program to certain eligible customers were determined to be guarantees under applicable accounting guidance. The Company recorded a liability for the estimated fair value of the guarantees at their inception. The Program expired on September 30, 2017, at which time the remaining guarantee liabilities of $1.1 were recognized as sales.

Valuation of Inventory

Inventories are valued at the lower of cost or net realizable value, determined by the first-in, first-out method. Inventory is recorded using standard cost, including material, labor and overhead costs. The Company periodically reviews inventories for potential impairment and adjust inventory to its net realizable value, based on quantities on hand and firm purchase commitments, expectations of future use, judgments based on quality control testing data and assessments of the likelihood of scrapping or obsoleting certain inventories based on future demand for its products and market conditions.

Long Lived Assets

Property and Equipment

Property and equipment, which primarily consist of office furniture and equipment, manufacturing equipment, scientific equipment, computer equipment, and leasehold improvements, are stated at cost, less accumulated depreciation. Property and equipment are depreciated over the estimated useful lives of the assets, generally three to seven years, using the straight-line method. Leasehold improvements are amortized over the lesser of the estimated useful lives of the assets or the remaining lease term. Maintenance and repair costs are expensed as incurred.

Patents

Costs associated with the purchase or licensing of patents associated with the Company’s commercialized products are capitalized. The Company reviews its capitalized patent costs periodically to determine that they have future value and an alternative future use. Costs related to patents that the Company is not actively pursuing for commercial purposes are expensed. The Company amortizes patent costs over the lesser of the duration of the patent term or the estimated useful lives of 10 years, beginning with the date the patents are issued or acquired.

The Company periodically re-evaluates the original assumptions and rationale utilized in the establishment of the carrying value and estimated lives of all of its long-lived assets, including property and equipment and acquired patents. The determinants used for this evaluation include management’s estimate of the asset’s ability to generate positive income from operations and positive cash flow in future periods as well as the strategic significance of the asset to the Company’s business objective. The Company has not recognized any impairment losses through December 31, 2018.

Deferred Rent

Rent expense on noncancelable leases containing known future scheduled rent increases is recorded on a straight-line basis over the term of the respective leases beginning when the Company takes possession of the leased property. The difference between rent expense and rent paid is accounted for as deferred rent. The current portion of deferred rent is included in other current liabilities on the Company’s consolidated balance sheet. Landlord improvement allowances and other such lease incentives are recorded as property and equipment and as deferred rent and are amortized on a straight-line basis as a reduction to rent expense.

Research and Development Costs

All research and development costs are charged to expense as incurred. Such costs include personnel-related costs, including stock-based compensation, supplies, license fees, development prototypes, outside design and testing services, depreciation, allocated facilities and information services, clinical trial costs, milestone payments under the Company’s development and commercialization agreements and other indirect costs.

Income Taxes

The Company uses the asset and liability method of accounting for income taxes. Deferred income tax assets or liabilities are recognized based on the temporary differences between financial statement and income tax bases of assets and liabilities using enacted tax rates in effect for the years in which the differences are expected to reverse. Tax law and rate changes are reflected in income in the period such changes are enacted. A valuation allowance is recorded when it is more likely than not that some of the deferred tax assets will not be realized. The Company includes interest and penalties related to income taxes, including unrecognized tax benefits, within income tax expense.

The Company’s income tax returns are based on calculations and assumptions that are subject to examination by the Internal Revenue Service and other tax authorities. In addition, the calculation of the Company’s tax liabilities involves dealing with uncertainties in the application of complex tax regulations. The Company recognizes liabilities for uncertain tax positions based on a two-step process. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates that it is more likely than not that the position will be sustained on audit, including resolution of related appeals or litigation processes, if any. The second step is to measure the tax benefit as the largest amount that is more than 50% likely of being realized upon settlement. While the Company believes it has appropriate support for the positions taken on its tax returns, the Company regularly assesses the potential outcomes of examinations by tax authorities in determining the adequacy of its provision for income taxes. The Company continually assesses the likelihood and amount of potential revisions and adjusts the income tax provision, income taxes payable and deferred taxes in the period in which the facts that give rise to a revision become known.

Significant judgment is required in determining the Company’s provision for income taxes, deferred tax assets and liabilities and the valuation allowance recorded against net deferred tax assets. Deferred tax assets and liabilities are determined using the enacted tax rates in effect for the years in which those tax assets are expected to be realized. A valuation allowance is established when it is more likely than not the future realization of all or some of the deferred tax assets will not be achieved. The evaluation of the need for a valuation allowance is performed on a jurisdiction-by-jurisdiction basis, and includes a review of all available positive and negative evidence. Factors reviewed include projections of pre-tax book income for the foreseeable future, determination of cumulative pre-tax book income after permanent differences, earnings history, and reliability of forecasting. The Company will continue to assess the need for a valuation allowance on its deferred tax assets by evaluating both positive and negative evidence that may exist. Any adjustment to the net deferred tax asset valuation allowance would be recorded in the statement of operations for the period that the adjustment is determined to be required.

The Company is required to file federal and state income tax returns in the United States and various other state jurisdictions and, starting with 2018, a corporation income tax return in Canada. The preparation of these income tax returns requires the Company to interpret the applicable tax laws and regulations in effect in such jurisdictions, which could affect the amount of tax paid by the Company. An amount is accrued for the estimate of additional tax liability, including interest and penalties, for any uncertain tax positions taken or expected to be taken in an income tax return. The Company reviews and updates the accrual for uncertain tax positions as more definitive information becomes available. For further information, see Note 7, Income Taxes.

Revenue Recognition

Revenue is generated primarily from sales of insulin pumps, disposable cartridges and infusion sets to individual customers and third-party distributors that resell the product to insulin-dependent diabetes customers. The Company is paid directly by customers who use the products, distributors and third-party insurance payors.

In January 2018, the Company adopted the Revenue from Contracts with Customers Standard which supersedes existing revenue guidance under U.S. GAAP and International Financial Reporting Standards. Pursuant to the Revenue from Contracts with Customers Standard’s core principle, subsequent to January 1, 2018, the Company recognizes revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those goods or services. The Company elected to implement this new standard utilizing the modified retrospective method. Under this approach, the Company applied the new standard to all new contracts initiated on or after the effective date, and, for contracts which had remaining obligations as of the effective date, the Company recorded an adjustment to the opening balance of accumulated deficit. The accounting for the significant majority of the Company’s revenues is not impacted by the new guidance. As a result, on January 1, 2018, the Company recorded a net reduction to accumulated deficit in the amount of $149,000, reflecting the accounting change.

Prior to the implementation of this new standard, revenue was recognized when persuasive evidence of an arrangement existed, delivery had occurred and title passed, the price was fixed or determinable, and collectability was reasonably assured.

Trade-In Rights

The Company launched a Technology Upgrade Program in 2016, which expired September 30, 2017. The trade-in rights associated with the Program were accounted for as guarantees or rights to return based on specific factors and circumstances, including the period of time the trade-in rights were exercisable, the likelihood that the trade-in rights would be exercised, and the amount of the specified-price trade-in value.

The Company determined that trade-in rights for t:slim G4 Pump customers were generally guarantees. The Company accounted for the guarantees under applicable accounting standards, which require a guarantor to recognize, at the inception of the guarantees, a liability for the estimated fair value of the obligation undertaken in issuing the guarantees. Subsequently, the initial liability recognized for the guarantees was reduced as the Company was released from the risk under the guarantees, which was when the trade-in right was exercised or the right expired. The guarantees were accounted for as an element of a multiple element arrangement. The estimated fair value of the guarantees was based on various economic and customer behavioral assumptions, including the probability that a trade-in right would be exercised, the specified trade-in amount, the expected fair value of the used t:slim G4 Pump at trade-in and the expected sales price of a t:slim X2. Upon expiration of the Program at September 30, 2017, the remaining guarantee liabilities of $1.1 were recognized as sales. There were no guarantee liabilities at December 31, 2018 or December 31, 2017.

The Company determined that t:slim Pump trade-in rights were in-substance rights to return products. Such rights to return were accounted for pursuant to the right of return accounting guidance. As the Company did not have sufficient history to reasonably estimate returns associated with trade-in rights, all eligible t:slim Pump sales between July 2016 and October 2016, which was when the company discontinued new shipments of t:slim, were recorded as deferred revenue until the trade-in right was exercised or the right expired. At December 31, 2018, the Company had no trade-in rights reserve balance. At December 31, 2017, there was $65,000, recorded as a trade-in rights reserve in deferred revenue on the accompanying consolidated balance sheet.

Revenue Recognition for Arrangements with Multiple Deliverables

The Company considers the individual deliverables in its product offering as separate performance obligations. The transaction price is determined based on the consideration expected to be received, based either on the stated value in contractual arrangements or the estimated cash to be collected in non-contracted arrangements. The Company allocates the consideration to the individual performance obligations and recognizes the consideration based on when the performance obligation is satisfied, considering whether or not this occurs at a point in time or over time. Generally, insulin pumps, cartridges, infusion sets and accessories are deemed performance obligations that are satisfied upon delivery, while access to the complementary products, such as the t:connect cloud-based data management application and the Tandem Device Updater, are considered performance obligations satisfied over the four-year warranty period of the insulin pumps. There is no standalone value for these complementary products. Therefore, the Company determines their value by applying the expected cost-plus margin approach and then allocates the residual to the insulin pumps. At December 31, 2018 and 2017, $3.8 million and $2.0 million were recorded as deferred revenue for these performance obligations that are satisfied over time.

Product Returns

The Company offers a 30-day right of return to its customers from the date of shipment of any of its insulin pumps, provided a physician’s confirmation of the medical reason for the return is received. Estimated allowances for sales returns are based on historical returned quantities as compared to pump shipments in those same periods of return. The return rate is then applied to the sales of the current period to establish a reserve at the end of the period. The return rates used in the reserve are adjusted for known or expected changes in the marketplace when appropriate. The allowance for product returns is recorded as a reduction of revenue and accounts receivable in the period in which the related sale is recorded. The amount recorded on the Company’s consolidated balance sheets for product return allowance was $0.3 million and $0.2 million at December 31, 2018 and 2017, respectively. Actual product returns have not differed materially from estimated amounts reserved in the accompanying consolidated financial statements.

Warranty Reserve

The Company generally provides a four-year warranty on its insulin pumps to end user customers and may replace any pumps that do not function in accordance with the product specifications. Insulin pumps returned to the Company may be refurbished and redeployed. Additionally, the Company offers a six-month warranty on disposable cartridges and infusion sets. Estimated warranty costs are recorded at the time of shipment. Warranty costs are estimated based on the current expected replacement product cost and expected replacement rates based on historical experience. The Company evaluates the reserve quarterly and makes adjustments when appropriate. Changes to the actual replacement rates and actual replacement product costs could have a material impact on the Company’s estimated liability.

At December 31, 2018 and December 31, 2017, the warranty reserve was $9.1 million and $5.6 million, respectively. The following table provides a reconciliation of the change in estimated warranty liabilities for the years ended December 31, 2018 and 2017:

	December 31,
(in thousands)	2018			2017
Balance at beginning of the year	$	5,640		$	5,690
Provision for warranties issued during the period		9,617			5,613
Settlements made during the period		(7,797	)		(6,742	)
Increases in warranty estimates		1,678			1,079
Balance at end of the year	$	9,138		$	5,640

Current portion	$	4,206		$	2,596
Non-current portion		4,932			3,044
Total	$	9,138		$	5,640

Stock-Based Compensation

Stock-based compensation cost is measured at the grant date based on the estimated fair value of the award, and the portion that is ultimately expected to vest is recognized as compensation expense over the requisite service period on a straight-line basis. The Company estimates the fair value of stock options issued under the Company’s 2013 Stock Incentive Plan or the 2013 Plan, and shares issued under the Company’s 2013 Employee Stock Purchase Plan, or the ESPP, using a Black-Scholes option-pricing model on the date of grant. The Black-Scholes option-pricing model requires the use of subjective assumptions including volatility, expected term, and risk-free interest rate. For awards that vest based on service conditions, the Company recognizes expense using the straight-line method less estimated forfeitures based on historical experience.

The Company records the expense for stock option grants to non-employees based on the estimated fair value of the stock options using the Black-Scholes option-pricing model. The fair value of non-employee awards is remeasured at each reporting period as the underlying awards vest unless the instruments are fully vested, immediately exercisable and nonforfeitable on the date of grant.

Warrant Liabilities

The Company accounts for certain warrants as a liability in the consolidated financial statements when they contain a provision within the warrant contracts that could require cash settlement in the event the Company did not have an active registration statement. The fair value of these warrants is remeasured at each financial reporting period with any changes in fair value being recognized as a component of other income (expense) in the accompanying statements of operations and comprehensive loss.

Advertising Costs

The Company expenses advertising costs as they are incurred. For the years ended December 31, 2018, 2017 and 2016, advertising costs were $0.9 million, $1.1 million, and $0.9 million, respectively.

Shipping and Handling Expenses

Shipping and handling expenses associated with product delivery are included within cost of sales in the Company’s statements of operations.

Comprehensive Loss

All components of comprehensive loss, including net loss, are reported in the consolidated financial statements in the period in which they are recognized. Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from non-owner sources, including unrealized gains and losses on marketable securities.

Net Loss Per Share

Basic net loss per share is calculated by dividing the net loss by the weighted average number of common shares that were outstanding for the period, without consideration for common stock equivalents. Diluted loss per share is calculated in accordance with the treasury stock method and reflects the potential dilution that would occur if securities or other contracts to issue common stock were exercised or converted to common stock. Dilutive common share equivalents are comprised of warrants, potential awards granted pursuant to the ESPP, and options outstanding under the Company’s other equity incentive plans. For warrants that are recorded as a liability in the accompanying consolidated balance sheet, the calculation of diluted loss per share requires that, to the extent the average market price of the underlying shares for the reporting period exceeds the exercise price of the warrants and the presumed exercise of such securities are dilutive to loss per share for the period, an adjustment to net loss used in the calculation is required to remove the change in fair value of the warrants from the numerator for the period. Likewise, an adjustment to the denominator is required to reflect the related dilutive shares, if any, under the treasury stock method. With the exception of the fourth quarter of 2018, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position. Refer to Note 11. Selected Quarterly Financial Data (Unaudited) for further details.

Potentially dilutive securities not included in the calculation of diluted net loss per share (because inclusion would be anti-dilutive) are as follows (in common stock equivalent shares, in thousands):

	Year Ended December 31,
	2018		2017		2016
Warrants for common stock		705		—		—
Common stock options		3,477		—		151
ESPP		4		—		2
		4,186		—		153

Accounting Pronouncements Issued and Not Yet Adopted

In February 2016, the FASB issued ASU 2016-02, Leases or ASU 2016-02. ASU 2016-02 and its related amendments (collectively referred to as ASC 842). The new guidance requires lessees to recognize right-of-use assets and corresponding lease liabilities for all leases with lease terms of greater than twelve months. It also changes the definition of a lease and expands the disclosure requirements of lease arrangements. In July 2018, the FASB added a transition option for implementation that allows companies to continue to use the legacy guidance in ASC 840, Leases, including its disclosure requirements, in the comparative periods presented in the year of adoption. The new accounting standard must be adopted using the modified retrospective approach and will be effective for the Company starting in the first quarter of fiscal 2019. We have elected the transition option and certain practical expedients, and expect that the adoption of this standard will result in a cumulative-effect transition adjustment for the recognition of right-of-use leased assets and corresponding lease liabilities of approximately $12 million on the consolidated balance sheet as of January 1, 2019 related to lease commitments, which consist primarily of operating leases for facilities, and will not restate prior periods. Deferred rent of $1.0 million and $3.8 million as of January 1, 2019 will be reclassified from other current liabilities and deferred rent long-term, respectively, to a reduction of the right-of-use leased assets in connection with the adoption of this standard. The Company is finalizing its implementation related to policies, processes and internal controls to comply with the guidance. The January 1, 2019 transition adjustment does not include amounts related to the facility lease entered into in January 2019 (see Note 12, Subsequent Event)

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, or ASU 2016-13, which modifies the measurement and recognition of credit losses for most financial assets and certain other instruments. The new standard requires the use of forward-looking expected credit loss models based on historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount, which may result in earlier recognition of credit losses under the new standard. The standard is effective for public business entities for annual periods beginning after December 15, 2019, and interim periods within those years. The Company plans to implement the new standard in the first quarter of 2020, and is in the process of reviewing its credit loss models to assess the impact of the adoption of the standard on its consolidated financial statements.

In August 2018, the FASB issued Accounting Standards Update No. 2018-13, Fair Value Measurement: Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, which adds and modifies certain disclosure requirements for fair value measurements. Under the new guidance, entities will no longer be required to disclose the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, or valuation processes for Level 3 fair value measurements. However, public companies will be required to disclose the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and related changes in unrealized gains and losses included in other comprehensive income. This update is effective for annual periods beginning after December 15, 2019, and interim periods within those periods, and early adoption is permitted. The Company is in the process of determining the impact the adoption will have on its Consolidated Financial Statements as well as whether to early adopt the new guidance.

In August 2018, the FASB issued ASU 2018-15, Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, or ASU 2018-15, that changes the accounting for implementation costs incurred in a cloud computing arrangement that is a service contract. The update aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The implementation costs should be presented as a prepaid asset in the balance sheet and expensed over the term of the hosting arrangement. The standard is effective for annual periods, including interim periods within those annual periods, beginning after December 15, 2019. Early adoption is permitted. The Company is in the process of assessing the impact of the adoption of the standard on its financial statements.

Financial Statement Information

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Financial Statement Information

3. Financial Statement Information

Short-term investments

The Company invests in investment securities, principally debt instruments of the U.S. Government, and financial institutions and corporations with strong credit ratings. The following represents a summary of the estimated fair value of short-term investments at December 31, 2018 and 2017 (in thousands):

At December 31, 2018	Maturity (in years)	Amortized Cost		Unrealized Gain		Unrealized Loss			Estimated Fair Value
Available-for-sale investment securities
Commercial paper	Less than 1	$	53,559	$	—	$	(22	)	$	53,537
U.S. Treasury securities	Less than 1		17,937		—		(2	)		17,935
Corporate debt securities	Less than 1		15,718		12		(1	)		15,729
Total		$	87,214	$	12	$	(25	)	$	87,201

At December 31, 2017	Maturity (in years)	Amortized Cost		Unrealized Gain		Unrealized Loss		Estimated Fair Value
Trading securities:
Mutual funds held for nonqualified deferred compensation plan participants		$	459	$	20	$	—	$	479
Total		$	459	$	20	$	—	$	479

Accounts Receivable

Accounts receivable consisted of the following (in thousands):

	December 31,
	2018			2017
Accounts receivable	$	37,030		$	22,071
Less allowance for doubtful accounts, and product returns		(1,837	)		(1,278	)
Total	$	35,193		$	20,793

The following table provides a reconciliation of the change in estimated allowance for doubtful accounts for the years ended December 31, 2018, 2017 and 2016 (in thousands):

	Allowance for Doubtful Accounts
Balance at December 31, 2015	$	221
Provision for doubtful accounts		632
Write-offs and adjustments, net of recoveries		(118	)
Balance at December 31, 2016	$	735
Provision for doubtful accounts	824
Write-offs and adjustments, net of recoveries		(524	)
Balance at December 31, 2017	$	1,035
Provision for doubtful accounts		1,448
Write-offs and adjustments, net of recoveries		(646	)
Balance at December 31, 2018	$	1,837

Inventory

Inventory consisted of the following at (in thousands):

	December 31,
	2018		2017
Raw materials	$	6,622	$	10,328
Work-in-process		2,710		3,812
Finished goods		10,564		12,853
Total	$	19,896	$	26,993

Property and Equipment

Property and equipment consisted of the following at (in thousands):

	December 31,
	2018			2017
Leasehold improvements	$	11,313		$	13,924
Computer equipment and software		8,745			9,040
Office furniture and equipment		4,415			4,686
Manufacturing and scientific equipment		18,306			17,505
		42,779			45,155
Less accumulated depreciation and amortization		(25,628	)		(25,524	)
Total	$	17,151		$	19,631

Depreciation and amortization expense related to property and equipment was $5.5 million, $6.5 million, and $5.2 million for the years ended December 31, 2018, 2017, and 2016, respectively.

Intangible Assets Subject to Amortization

Intangible assets subject to amortization consist of patents purchased or licensed that are related to the Company’s commercialized products. The following represents the capitalized patents at December 31, 2018 and 2017 (in thousands):

	December 31,
	2018			2017
Gross amount	$	3,247		$	3,247
Accumulated amortization		(2,117	)		(1,790	)
Total	$	1,130		$	1,457
Weighted average remaining amortization period (in months)		42			54

Amortization expense related to intangible assets subject to amortization amounted to $0.3 million for each of the years ended December 31, 2018, 2017, and 2016. The amortization expense is recorded in cost of sales in the consolidated statement of operations. The estimated annual amortization is $0.3 million for periods 2019 through 2021, and $0.2 million in 2022.

Fair Value Measurements

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

4. Fair Value Measurements

Authoritative guidance on fair value measurements defines fair value, establishes a consistent framework for measuring fair value, and expands disclosures for each major asset and liability category measured at fair value on either a recurring or a nonrecurring basis. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the authoritative guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows:

Level 1:		Observable inputs such as unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities.

Level 2:		Inputs, other than quoted prices in active markets, that are observable either directly or indirectly for substantially the full term of the asset or liability.

Level 3:		Unobservable inputs in which there is little or no market data and that are significant to the fair value of the assets or liabilities, which require the reporting entity to develop its own valuation techniques that require input assumptions.

The following table presents information about the Company’s financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2018 and 2017, and indicates the fair value hierarchy of the valuation techniques utilized by the Company to determine such fair value (in thousands):

			Fair Value Measurements at
			December 31, 2018
	December 31, 2018		Level 1		Level 2		Level 3
Assets
Cash equivalents⁽¹⁾	$	37,373	$	37,373	$	—	$	—
Commercial paper		53,537		—		53,537		—
U.S. Treasury securities		17,935		17,935		—		—
Corporate debt securities		15,729				15,729		—
Total assets	$	124,574	$	55,308	$	69,266	$	—
Liabilities
Common stock warrants	$	17,926	$	—	$	—	$	17,926
Total liabilities	$	17,926	$	—	$	—	$	17,926

			Fair Value Measurements at
			December 31, 2017
	December 31, 2017		Level 1		Level 2		Level 3
Assets
Cash equivalents ⁽¹⁾	$	23,700	$	23,700	$	—	$	—
Mutual funds held for nonqualified deferred compensation plan participants⁽²⁾		479		479		—		—
Total assets	$	24,179	$	24,179	$	—	$	—
Liabilities
Common stock warrants	$	5,432	$	—	$	—	$	5,432
Deferred compensation ⁽²⁾		479	$	479	$	—	$	—
Total liabilities	$	5,911	$	479	$	—	$	5,432

(1)

Cash equivalents included money market funds and commercial paper with a maturity of three months or less from the date of purchase. As of December 31, 2017, $13.7 million was included as a component of cash and cash equivalents on the balance sheet, and $10.0 million was classified as restricted cash – long-term.

(2)

The deferred compensation plan was directed by the Company and structured as a Rabbi Trust for the benefit of certain executives and non-employee directors. The investment assets of the Rabbi Trust were valued using quoted market prices multiplied by the number of shares held in each trust account. The related deferred compensation liability at December 31, 2017 represented the fair value of the investment assets. The Company cancelled the deferred compensation plan in 2017 and all deferred compensation amounts were distributed to participants during the second quarter of 2018.

The Company’s Level 2 financial instruments are valued using market prices on less active markets with observable valuation inputs such as interest rates and yield curves. The Company obtains the fair value of Level 2 financial instruments from quoted market prices, calculated prices or quotes from third-party pricing services. The Company validates these prices through independent valuation testing and review of portfolio valuations provided by the Company’s investment managers. There were no transfers between Level 1 and Level 2 securities during the years ended December 31, 2018 and 2017.

Level 3 liabilities at December 31, 2018 and 2017 include the Series A and Series B common stock warrants issued by the Company in connection with the public offering of common stock in October 2017. The Series A warrants have a term of five years and initially provided holders the right to purchase 4,630,000 shares of the Company’s common stock at an exercise price of $3.50 per share. The Series B warrants had a term of six months and initially provided holders the right to purchase 4,630,000 shares of the Company’s common stock at an exercise price of $3.50 per share. The Series A and Series B warrants were initially valued in the aggregate amount of $6.5 million on the date of issuance utilizing a Black-Scholes pricing model. As of December 31, 2018, there were Series A warrants to purchase 510,785 shares of common stock outstanding and no Series B warrants outstanding.

The Company reassesses the fair value of the outstanding Series A and Series B warrants at each reporting date utilizing a Black-Scholes pricing model. Inputs used in the pricing model include estimates of stock price volatility, expected warrant life and risk-free interest rate. The Company develops its estimates based on publicly available historical data. The assumptions used to estimate the fair values of the common stock warrants at December 31, 2018 and 2017 are presented below:

	Series A Warrants
	December 31, 2018			December 31, 2017
Risk-free interest rate		3.0	%		2.2	%
Expected dividend yield		0.0	%		0.0	%
Expected volatility		78.3	%		63.5	%
Expected term (in years)		3.8			4.8

	Series B Warrants
	December 31, 2018			December 31, 2017
Risk-free interest rate	N/A				1.4	%
Expected dividend yield	N/A				0.0	%
Expected volatility	N/A				80.3	%
Expected term (in years)	N/A				0.3

The following table presents a summary of changes in fair value of the Company’s total Level 3 financial assets for the years ended December 31, 2018 and 2017:

	2018			2017
Balance at beginning of period	$	5,432		$	6,453
Increase (decrease) in fair value included in change in fair value of common stock warrants		66,494			(1,021	)
Decrease in fair value from warrants exercised during the period		(54,000	)		—
Balance at end of period	$	17,926		$	5,432

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Term Loan Agreement

12 Months Ended

Dec. 31, 2018

Debt Disclosure [Abstract]

Term Loan Agreement

5. Term Loan Agreement

In August 2018, the Company fully repaid the term loan made by CRG pursuant to the Term Loan Agreement and terminated the agreement. The term loan was collateralized by all assets of the Company. The balance of the outstanding debt at the time of repayment was $82.7 million. The repayment included approximately $1.1 million in accrued interest and $5.0 million in associated financing fees that became due. As a result of the repayment, the Company did not have any borrowings outstanding under the Term Loan Agreement as of December 31, 2018. The Company had aggregate borrowings under the Term Loan Agreement of $82.7 million as of December 31, 2017. Notes payable-long term on the accompanying consolidated balance sheet reflected these aggregate borrowings, offset by a $6.2 million debt discount associated with the financing fees and certain debt issuance costs at December 31, 2017. Such discounts were amortized to interest expense over the term of the loan using the effective interest method. At the time of repayment, the remaining balance of $5.3 million was accelerated and recognized as a loss on extinguishment of debt in the consolidated statement of operations for the year ended, December 31, 2018.

Under the Term Loan Agreement, interest was payable at the Company’s option, (i) in cash at a rate of 11.5% per annum, or (ii) at a rate of 9.5% of the 11.5% per annum in cash and 2.0% of the 11.5% per annum or the PIK Loan to be added to the principal of the loan and subject to accruing interest. Interest-only payments were due quarterly on March 31, June 30, September 30 and December 31 of each year of the interest-only payment period, which would have ended on December 31, 2019. The principal balance was due in full at the end of the term of the loan, which was March 31, 2020, or the Maturity Date. The Company had elected to pay interest in cash at a rate of 11.5% per annum through September 30, 2015. From October 1, 2015 through December 31, 2017, the Company elected to pay interest in cash at a rate of 9.5% per annum and for a rate of 2.0% per annum to be added to the principal of the loan. As a result, $2.7 million was added to the principal of the loan during that time period, collectively, the PIK Loans.

The Company entered into a series of amendments to the Term Loan Agreement in 2016, 2017 and 2018, which included the addition of a financing fee payable at the maturity of the Company’s loans, the issuance of 193,788 ten-year warrants to CRG to purchase shares of the Company’s common stock at an exercise price of $23.50 per share and certain other minimum financing covenants. The financing fee was applicable to the entire aggregate principal amount of borrowings outstanding, including total PIK Loans issued. The Company treated the execution of each of the Third, Fourth and Fifth Amendments as a modification for accounting purposes. The present value of the future cash flows under these amendments did not exceed the present value of the future cash flows under the previous terms by more than 10%.

At December 31, 2017, the Company had accrued $4.1 million for the financing fee of 5%, which was subsequently increased to $5.0 million, or 6%, in February 2018. These fees were included in other long-term liabilities and as contra-debt in notes payable-long term on the accompanying consolidated balance sheet.

Stockholders' Equity (Deficit)

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

Stockholders' Equity (Deficit)

6. Stockholders’ Equity (Deficit)

Public Offerings

In the first quarter of 2017, the Company completed a registered public offering of 1,850,000 shares of common stock at a public offering price of $12.50 per share. The gross proceeds from the offering were approximately $23.1 million, before deducting underwriting discounts and commissions and other offering expenses.

From July 2017 through September 2017, the Company sold 464,108 shares of common stock under our “at-the-market” offering program at prices ranging from $5.64 to $10.54. The gross proceeds from the offering were $4.3 million, before deducting underwriting discounts and commissions and other offering expenses.

In the fourth quarter of 2017, the Company completed the October Financing, pursuant to which it sold 4,630,000 shares of common stock, Series A warrants to purchase up to 4,630,000 shares of our common stock and Series B warrants to purchase up to 4,630,000 shares of common stock at a public offering price of $3.50 per share and accompanying warrants. The gross proceeds from the October Financing were approximately $16.2 million, before deducting underwriting discounts and commissions and other offering expenses.

In the first quarter of 2018, the Company completed a registered public offering of 34,500,000 shares of common stock at a public offering price of $2.00 per share. The gross proceeds from the offering were approximately $69.0 million, before deducting underwriting discounts and commissions and other offering expenses.

In the third quarter of 2018, the Company completed a public offering of 4,035,085 shares of common stock at a public offering price of $28.50 per share. The gross proceeds to the Company from the offering were $115.0 million, before deducting underwriting discounts and commissions and other offering expenses payable by the Company.

Stock Plans

In September 2006, the Company adopted the Company’s 2006 Stock Incentive Plan, or the 2006 Plan, under which, as amended, 268,561 shares of common stock were reserved for issuance to employees, non-employee directors and consultants of the Company. The 2006 Plan was closed in 2013 with the approval of the 2013 Stock and no further options will be granted under the 2006 Plan.

In October 2013, the Company’s board of directors approved the 2013 Plan. The 2013 Plan became effective immediately prior to the completion of the initial public offering. An initial 480,900 shares of common stock were reserved for issuance under the 2013 Plan. Under the 2013 Plan, the Company may grant stock options, stock appreciation rights, restricted stock and restricted stock units to individuals who are then employees, officers, directors or consultants of the Company. The 2013 Plan also included an “evergreen” provision, which automatically increased the shares available for issuance January 1 of each year by 4% of common shares outstanding. Accordingly, the shares available for issuance under the 2013 Plan were increased by 404,776 shares and 124,382 shares on January 1, 2018 and 2017, respectively. In June 2018, the Company received approval from its stockholders to increase the number of shares of common stock reserved under the 2013 Plan by 5,500,000 shares, and to remove the evergreen provision.

The Company issued 8,603,321 shares of common stock upon the exercise of warrants, and 136,042 shares of common stock upon the exercise of stock options during the year ended December 31, 2018. The Company did not issue any shares of common stock upon the exercise of warrants, and issued 24,406 shares of common stock upon the exercise of stock options during the year ended December 31, 2017.

As of December 31, 2018, 969,445 shares were available for future issuance under the 2013 Plan, and options to purchase 5,763,192 shares have been granted and are outstanding under the 2006 Plan and 2013 Plan.

Common Stock Options

The maximum term of stock options granted under the 2006 Plan and 2013 Plan is ten years. The options generally vest 25% on the first anniversary of the original vesting date, with the balance vesting monthly over the remaining three years.

The following table summarizes stock option activities for the 2006 Plan and 2013 Plan:

	Total Options			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2016		822,265		$	84.05		7.92	$	1,593
Granted		615,067		$	4.69
Exercised		(24,406	)	$	11.06			$	338
Canceled/forfeited/expired		(81,657	)	$	110.21
Outstanding at December 31, 2017		1,331,269		$	47.11		8.08	$	—
Granted		4,730,956		$	20.34
Exercised		(136,042	)	$	7.55			$	3,953
Canceled/forfeited/expired		(162,991	)	$	45.46			$	1,466
Outstanding at December 31, 2018		5,763,192		$	23.61		8.94	$	116,988
Vested and expected to vest at December 31, 2018		5,643,473		$	23.73		8.94	$	114,547
Exercisable at December 31, 2018		1,215,287		$	43.40		7.34	$	25,852

Employee Stock Purchase Plan

In October 2013, the Company adopted the ESPP, which enables eligible employees to purchase shares of the Company’s common stock using their after-tax payroll deductions, subject to certain conditions. The ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the Code. Eligible employees may contribute, normally through payroll deductions, up to 15% of their earnings for the purchase of common stock under the ESPP. The purchase price of common stock under the ESPP is the lesser of: (a) 85% of the fair market value of a share of the Company’s common stock on the first date of an offering or (b) 85% of the fair market value of a share of the Company’s common stock on the date of purchase. Generally, the ESPP consists of a two-year offering period with four six-month purchase periods.

The ESPP initially authorized the issuance of 55,600 shares of common stock pursuant to purchase rights granted to employees. The number of shares of common stock reserved for issuance increased on January 1 of each calendar year, from January 1, 2014 through January 1, 2018, by the lesser of (a) one percent (1%) of the number of shares issued and outstanding on the immediately preceding December 31, or (b) such lesser number of shares as determined by the Administrator. On January 1, 2017 and 2018, the number of shares of common stock reserved for issuance under the ESPP was automatically increased by 101,194 and 31,096 shares respectively. In the years ended December 31, 2018 and 2017, 80,581 shares and 38,929 shares of our common stock, respectively, were purchased under the ESPP.

The Company announced the suspension of the ESPP as of May 16, 2017 due to a lack of available shares. The suspension was accounted for as a cancellation of an award with no consideration. The previously unrecognized compensation cost as of the suspension date of $2.4 million was fully expensed during the second quarter of 2017. In June 2018, the Company received approval from its stockholders to increase the number of shares reserved for issuance under the ESPP by an additional 2,000,000 shares and to remove the evergreen provision.

In the years ended December 31, 2018 and 2017, 80,581 shares and 38,929 shares of our common stock, respectively, were purchased under the ESPP. As of December 31, 2018, 2,020,626 shares remained available for issuance under the ESPP.

Stock-Based Compensation.

The compensation cost that has been included in the consolidated statement of operations for all stock-based compensation arrangements was as follows (in thousands):

	Year Ended December 31,
	2018		2017		2016
Cost of sales	$	2,581	$	1,360	$	1,016
Selling, general & administrative		16,824		10,020		9,360
Research and development		4,331		1,248		1,284
Total	$	23,736	$	12,628	$	11,660

The total stock-based compensation capitalized as part of the cost of the Company’s inventory was $0.2 million and $0.2 million at December 31, 2018 and 2017, respectively.

There were no stock option grants to non-employees and no expense during the years ended December 31, 2018, 2017 and 2016.

At December 31, 2018, the total unamortized stock-based compensation expense of approximately $45.3 million will be recognized over the remaining weighted average vesting term of approximately 1.7 years.

The assumptions used in the Black-Scholes option-pricing model are as follows:

	Stock Option
	Year Ended December 31,
	2018			2017			2016
Weighted average grant date fair value (per share)	$	12.94		$	2.65		$	24.30
Risk-free interest rate		2.8	%		2.1	%		1.7	%
Expected dividend yield		0.0	%		0.0	%		0.0	%
Expected volatility		71.4	%		60.8	%		57.5	%
Expected term (in years)		5.7			5.8			5.8

	ESPP
	Year Ended December 31,
	2018			2017⁽¹⁾
Weighted average grant date fair value (per share)	$	13.48		N/A
Risk-free interest rate		2.5	%	N/A
Expected dividend yield		0.0	%	N/A
Expected volatility		81.2	%	N/A
Expected term (in years)		1.25		N/A

(1)

There were no grants made pursuant to the ESPP during the year ended December 31, 2017.

Risk-free Interest Rate. The risk-free interest rate assumption was based on the United States Treasury’s rates for U.S. Treasury zero-coupon bonds with maturities similar to those of the expected term of the award being valued.

Expected Dividend Yield. The expected dividend yield is zero because the Company has never declared or paid any cash dividends and does not presently plan to pay cash dividends in the foreseeable future.

Expected Volatility. The expected volatility is estimated based on a weighted-average volatility of the Company’s actual historical volatility since its initial public offering in November 2013 and the historical stock volatilities of a peer group of similar companies whose share prices are publicly available. The Company continues to use the historical volatility of peer entities due to the lack of sufficient historical data of its stock price. The peer group consisted of other publicly traded companies in the same industry and in a similar stage of development. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available.

Expected Term. The Company utilized the simplified method for estimating the expected term of stock option grants. Under this approach, the weighted-average expected term is presumed to be the average of the vesting term and the contractual term of the option. The Company estimates the expected term of the ESPP using expected life for each tranche during the two-year offering period.

The Company also estimates forfeitures at the time of grant, and revises those estimates in subsequent periods if actual forfeitures differ from its estimates. Historical data was used to estimate pre-vesting option forfeitures and record stock-based compensation expense only for those awards that are expected to vest.

Common Stock Reserved for Future Issuance

The following shares of common stock were reserved for future issuance at December 31, 2018 (in thousands):

Common stock warrants outstanding			804
Stock options issued and outstanding			5,769
Authorized for future option grants			969
Employee stock purchase plan			2,021
			9,563

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

7. Income Taxes

The expense (benefit) for income taxes reconciles to the amount computed by applying the federal statutory rate to income before taxes as follows (in thousands):

	Year Ended December 31,⁽¹⁾
	2018			2017			2016
Income tax benefit at federal statutory rate	$	(25,738	)	$	(24,829	)	$	(28,362	)
State income tax, net of federal benefit		(1,649	)		(2,034	)		(2,393	)
Warrants revaluation		13,964			(347	)		—
Research and development credits		(1,425	)		(480	)		(720	)
Stock-based compensation		1,362			3,214			1,686
Tax Cuts and Jobs Acts		—			51,577			—
Other		681			138			456
Change in valuation allowance		12,856			(27,231	)		29,318
Income tax expense (benefit)	$	51		$	8		$	(15	)

(1)

For the year ended December 31, 2018 as a result of the Tax Cuts and Jobs Act, the statutory rate was 21%. For the years ended December 31, 2017 and 2016, the statutory rate was 34%.

Significant components of the Company’s net deferred income tax assets at December 31, 2018 and 2017 are shown below (in thousands). A valuation allowance has been recorded to offset the net deferred tax asset as of December 31, 2018 and 2017, as the realization of such assets does not meet the more-likely-than-not threshold.

	December 31,
	2018			2017
Deferred tax assets:
Net operating loss (NOL) carryforwards	$	85,761		$	81,483
Research and development tax credits carryforwards		4,942			3,517
Capitalized research and development expenses		10,759			12,746
Accrued compensation		13,816			8,809
Other		8,238			4,139
Total deferred tax assets		123,516			110,694
Less valuation allowance		(123,516	)		(110,694	)
Net deferred tax assets	$	—		$	—

As of December 31, 2018, the Company has accumulated federal, state and foreign NOL carryforwards of approximately $352.7 million, $313.5 million, and $1.1 million, respectively, not considering the annual limitations of Section 382 of the Internal Revenue Code of 1986, as amended, or the Code, as discussed below. The federal and state tax loss carryforwards begin to expire in 2026 and 2019, respectively, unless previously utilized. The remaining California NOL carry forwards of $183.9 million will expire beginning in 2028. The foreign tax loss carryforwards begin to expire in 2038, unless previously utilized.

The Company also has federal and California research credit carryforwards of approximately $5.7 million and $6.3 million, respectively. The federal research credit carryforwards will begin expiring in 2028 unless previously utilized. The California research credit will carry forward indefinitely.

In March 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Shared-Based Payment Accounting (''ASU 2016-09''). ASU 2016-09 simplifies how several aspects of share-based payments are accounted for and presented in the consolidated financial statements. ASU 2016-09 is effective for public companies and was adopted by the Company in 2017. The Company has excess tax benefits for which a benefit could not be previously recognized of approximately $1.8 million. Upon adoption, the balance of the unrecognized excess tax benefits was reversed with the impact recorded to retained earnings which was fully offset by a change to the valuation allowance.

Utilization of the Company's net operating loss carryforwards may be subject to a substantial annual limitation due to ownership change limitations provided by Section 382 of the Internal Revenue Code of 1986, as amended, and similar state provisions. The annual limitations may result in the expiration of net operating loss carryforwards before utilization. The Company has started but has not completed an analysis to determine whether its net operating losses and credits generated through December 31, 2018 are likely to be limited by Section 382. Based on preliminary results of this analysis, the Company anticipates that an ownership change as defined under Section 382 may have occurred in 2018 and that the resulting limitation would significantly reduce the Company’s ability to utilize its net operating loss and credit carryovers before they expire. Additionally, future ownership changes under Section 382 may also limit the Company's ability to fully utilize any remaining tax benefits. The Company's net deferred income tax assets have been fully offset by a valuation allowance. Therefore, any resulting reduction to the Company's net operating loss and credit carryovers once the analysis is complete will be fully offset by a corresponding reduction of the valuation allowance and there would be no impact on the Company's balance sheet, statement of operations, or cash flows.

The evaluation of uncertainty in a tax position is a two-step process. The first step involves recognition. The Company determines whether it is more likely than not that a tax position will be sustained upon tax examination, including resolution of any related appeals or litigation, based on only the technical merits of the position. The technical merits of a tax position are derived from both statutory and judicial authority (legislation and statutes, legislative intent, regulations, rulings, and case law) and their applicability to the facts and circumstances of the tax position. If a tax position does not meet the more-likely-than-not recognition threshold, the benefit of that position is not recognized in the financial statements. The second step is measurement. A tax position that meets the more-likely-than-not recognition threshold is measured to determine the amount of benefit to recognize in the financial statements. The tax position is measured as the largest amount of benefit that is greater than 50% likely of being realized upon ultimate resolution with a taxing authority.

The following table summarizes the activity related to the Company’s gross unrecognized tax benefits at the beginning and end of the years ended December 31, 2018, 2017 and 2016 (in thousands):

	Year Ended December 31,
	2018		2017			2016
Gross unrecognized tax benefits at the beginning of the year	$	8,121	$	8,167		$	7,594
Increases related to current year positions		644		411			580
Increases (decreases) related to prior year positions		59		(457	)		(7	)
Gross unrecognized tax benefits at the end of the year	$	8,824	$	8,121		$	8,167

As of December 31, 2018, the Company had $7.3 million of unrecognized tax benefits that, if recognized and realized would impact the effective tax rate, subject to the valuation allowance.

The Company’s practice is to recognize interest and penalties related to income tax matters in income tax expense. The Company had no accrual for interest and penalties on the Company’s consolidated balance sheets and has not recognized interest and penalties in the statements of operations for the years ended December 31, 2018 and 2017. The Company does not expect any significant increases or decreases, other than the potential reduction as a result of the Section 382 limitation, to its unrecognized tax benefits within the next 12 months.

The Company is subject to taxation in the United States and various other state jurisdictions and, starting with 2018, Canada. For the year ended December 31, 2018, the domestic and foreign components of loss before income taxes were $122.0 million and $1.0 million, respectively. Prior to 2018, the losses were all domestic. The Company’s tax years from 2006 (inception) are subject to examination by the United States and state authorities due to the carry forward of unutilized NOLs and research and development credits.

In December 2017, the Tax Cuts and Jobs Act, or the 2017 Act, was enacted. The 2017 Tax Act includes a number of changes to existing U.S. tax laws that impact the company, most notably a reduction of the U.S. corporate income tax rate from 35 percent to 21 percent for tax years beginning after December 31, 2017. The 2017 Tax Act also provides for the acceleration of depreciation for certain assets placed in service after September 27, 2017 as well as prospective changes beginning in 2018, including additional limitations on executive compensation, limitations on the deductibility of interest and capitalization of research and development expenditures.

Reduction of the U.S. Corporate Income Tax Rate: The Company measures deferred tax assets and liabilities using enacted tax rates that will apply in the years in which the temporary differences are expected to be recovered or paid. Accordingly, the Company's deferred tax assets and liabilities were remeasured to reflect the reduction in the U.S. corporate income tax rate from the highest graduated tax 35% to a 21% flat tax. As a result of the tax rate, in 2017 we recorded a decrease to our deferred tax assets of $51.6 million and the valuation allowance was decreased by the same amount, resulting in no net tax expense.

The Act will no longer allow deductions for compensation in excess of $1.0 million for certain employees, even if paid as commissions or performance-based compensation. It also subjects the principal executive officer, principal financial officer and three other highest paid officers to the limitation and once the individual becomes a covered person, the individual will remain a covered person for all future years.

The Act allows Companies to claim bonus depreciation to accelerate the expensing of the cost of certain qualified property placed in service after September 27, 2017 and before January 1, 2024. The Company recognized a provisional increase in net deferred tax liabilities attributable to the accelerated depreciation for certain assets placed into service after September 27, 2017. Due to the valuation allowance, the provisional adjustments have no impact on income tax expense or income tax payable.

The company recognized the income tax effects of the 2017 Tax Act in its 2017 financial statements in accordance with Staff Accounting Bulletin No. 118, which provides SEC staff guidance for the application of ASC Topic 740, Income Taxes, in the reporting period in which the 2017 Act was signed into law. In accordance with Staff Accounting Bulletin No. 118, as of December 31, 2018, we have completed our accounting for the tax effects of enactment of the Act and no adjustments to the provisional income tax effects were required.

Collaborations

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Collaborations

8. Collaborations

DexCom Development and Commercialization Agreement

In February 2012, the Company entered into a Development and Commercialization Agreement (the “DexCom Agreement”) with DexCom, Inc., or DexCom, for the purpose of collaborating on the development and commercialization of an integrated system which incorporates the t:slim Insulin Delivery System with DexCom’s proprietary CGM system.

Between 2012 and 2015, the Company paid to DexCom a total of $3.0 million in licensing fees. Additionally, upon commercialization of t:slim G4, and as compensation for non-exclusive license rights, under the original DexCom Agreement, the Company agreed to pay DexCom a royalty calculated at $100 per integrated system sold.

In September 2015, the Company entered into an amendment to the DexCom Agreement, or the Amendment. Pursuant to the Amendment, in lieu of the $100 royalty payment for each integrated system sold, the Company agreed to commit $100 of each t:slim G4 integrated system sold to incremental marketing activities associated with t:slim G4 integrated systems that are in addition to a level of ordinary course marketing activities or marketing activities to support other Company and DexCom jointly funded development projects. The committed marketing fund is recognized as cost of sales and other current liabilities in the period the related t:slim G4 Pump sale is recorded. The Company recorded such marketing fund commitment of $0.1 million and $1.1 million in the years ended December 31, 2018 and 2017, respectively.

Employee-Benefits

12 Months Ended

Dec. 31, 2018

Defined Contribution Pension And Other Postretirement Plans Disclosure [Abstract]

Employee Benefits

9. Employee Benefits

Employee 401(k) Plan

The Company has a defined contribution 401(k) plan for employees who are at least 18 years of age. Employees are eligible to participate in the plan beginning on the first day of the calendar month following their date of hire. Unless they affirmatively elect otherwise, employees are automatically enrolled in the plan following 30 days from date of rehire or entry date. Under the terms of the plan, employees may make voluntary contributions as a percent of compensation. The Company does not provide a matching contribution program.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

10. Commitments and Contingencies

From time to time, the Company may be subject to legal proceedings or regulatory encounters or other matters arising in the ordinary course of business, including actions with respect to intellectual property, employment, product liability and contractual matters. In connection with these matters, the Company regularly assesses the probability and range of possible loss based on the developments in these matters. A liability is recorded in the consolidated financial statements if it is determined that it is probable that a loss has been incurred, and that the amount or range of the loss can be reasonably estimated. Because of the uncertainties related to any pending actions, the Company is currently unable to predict their ultimate outcome, and, with respect to any legal proceeding or claim where no liability has been accrued, to make a meaningful estimate of the reasonably possible loss or range of loss that could result from an adverse outcome. At December 31, 2018 and 2017, there were no legal proceedings, disputes, or other claims for which a material loss was considered probable or for which the amount or range of loss was reasonably estimable.

Operating leases

Under a noncancelable operating lease agreement, or the Existing Operating Lease, the Company leases manufacturing, laboratory and general office spaces in San Diego, California. On December 27, 2017, the Company entered into an amendment to the Existing Operating Lease which terminated the lease with respect to the building located at 11045 Roselle Street as of January 31, 2018, and extended the Existing Operating Lease term for the remaining buildings through May 2022. The building located at 11045 Roselle Street, which primarily housed the Company’s manufacturing and related operations, was replaced by a facility located on Barnes Canyon Road in San Diego, California, collectively, the Barnes Canyon Lease. Pursuant to the amendment, the Company has the right to terminate the lease on the remaining buildings effective May 31, 2021 upon (i) delivery of written notice to the landlord no later than June 1, 2020, and (ii) an early termination payment to the landlord of approximately $0.4 million.

In connection with the Existing Operating Lease, the Company has a $0.3 million unsecured standby letter of credit arrangement with a bank under which the landlord of the building is the beneficiary. The expiration of the standby letter of credit is July 15, 2022.

On June 30, 2016, the Company entered into the Barnes Canyon Lease. The Barnes Canyon Lease is scheduled to expire in November 2023. The Company will also have a one-time option to extend the term of the lease for a period of not less than 36 months and not greater than 60 months, by delivering notice to the landlord at least nine months and not more than 12 months prior to the expiration of the lease.

The Barnes Canyon Lease allowed for a Tenant Improvement Allowance, or the TI Allowance of up to approximately $3.4 million to be applied to non-structural improvements to the building. Amounts utilized by the Company from the TI Allowance are subject to an interest accrual at a rate of 8.0% per annum and must be repaid in full during the lease term in monthly installments, or the TI Rent concurrently with the base rent. During the years ended December 31, 2017 and 2016, costs incurred for non-structural improvements to the facility were $3.9 million and $1.0 million, respectively, of which $2.6 million and $0.7 million, respectively, were funded by the landlord. The Company retains the right at any time during the lease term to prepay all or any portion of the TI Allowance drawn and outstanding without penalty, in which case the outstanding TI Rent would be reduced to reflect the TI Allowance prepayment and interest would cease to accrue on the prepaid portion of the TI Allowance.

The monthly rent, except TI Rent mentioned above, increases by a fixed percentage each year on the anniversary of the respective rent commencement date of the Existing Operating Lease and Barnes Canyon Lease. The difference between the straight-line expense over the term of the lease and actual amounts paid are recorded as deferred rent. Deferred rent arising from rent escalation provisions and lease incentives totaled $4.8 million and $5.6 million at December 31, 2018 and 2017, respectively. Rent expense for the three years ended December 31, 2018, 2017 and 2016, was $2.6 million, $3.5 million, and $3.1 million, respectively.

Future minimum payments under the aforementioned noncancelable operating leases for each of the five succeeding years following December 31, 2018 are as follows (in thousands):

2019	$	2,743
2020		2,858
2021		2,944
2022		1,644
2023		642
Thereafter		—
	$	10,831

Not included in the table above is the Barnes Canyon Lease TI Rent, which totaled $0.7 million and $0.4 million during the years ended December 31, 2018 and 2017, respectively. TI Rent will be approximately $0.7 million for each of the years ended December 31, 2019 through 2023.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

11. Selected Quarterly Financial Data (Unaudited)

The following financial information reflects all normal recurring adjustments that are, in the opinion of management, necessary for a fair statement of the results of the interim periods. Quarterly financial information for fiscal 2018 and 2017 is presented in the following table, in thousands, except per share data:

	For the Quarter Ending
	March 31			June 30			September 30			December 31
2018:
Revenue	$	27,277		$	34,126		$	46,264		$	76,199
Gross profit	$	11,404		$	15,087		$	21,796		$	41,535
Operating expenses	$	26,889		$	29,084		$	37,505		$	40,975
Operating income (loss)	$	(15,485	)	$	(13,997	)	$	(15,709	)	$	560
Net income (loss)	$	(32,693	)	$	(59,359	)	$	(34,245	)	$	3,686
Basic net income (loss) per share ⁽¹⁾	$	(1.82	)	$	(1.17	)	$	(0.62	)	$	0.06
Diluted net income (loss) per share ⁽¹⁾	$	(1.82	)	$	(1.17	)	$	(0.62	)	$	0.02

2017:
Revenue	$	18,977		$	21,327		$	27,003		$	40,294
Gross profit	$	6,753		$	8,001		$	11,873		$	17,468
Operating expenses	$	27,979		$	26,970		$	25,039		$	27,050
Operating loss	$	(21,226	)	$	(18,969	)	$	(13,166	)	$	(9,583	)
Net loss	$	(23,792	)	$	(21,801	)	$	(16,034	)	$	(11,406	)
Basic and diluted net loss per share ⁽¹⁾	$	(7.46	)	$	(4.36	)	$	(3.09	)	$	(1.23	)

(1)

Net income (loss) per share is computed independently for each quarter and the full year based upon the respective average shares outstanding in each period. Therefore, the sum of the quarterly per-share calculations may not equal the reported annual per share amounts.

Subsequent Event

12 Months Ended

Dec. 31, 2018

Subsequent Events [Abstract]

Subsequent Event

12. Subsequent Event

In January 2019, the Company entered into a lease agreement for 25,332 square feet of additional general administrative office space located at 10935 Vista Sorrento Parkway, San Diego, California. Subject to limited exceptions, the initial lease term is expected to commence on the later of (i) March 1, 2019, or (ii) the date on which the landlord substantially completes certain specified work related to tenant improvements, such date the Commencement Date, and will expire 42 months from the first day of the first full month following the Commencement Date. The Company also has a one-time option to extend the term of the lease for a period of five years by delivering prior written notice to the Landlord in accordance with the terms of the lease. Future minimum payments under the lease, which include reimbursement of certain landlord operating expenses, are approximately $3.5 million.

Organization and Basis of Presentation (Policies)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

The Company

Basis of Presentation and Principles of Consolidation

Reverse Stock Split

Reclassifications

Certain reclassifications of prior year amounts related to the presentation of restricted cash on the statement of cash flows have been made to conform to the current year presentation.

Use of Estimates

Segment Reporting

Cash Equivalents

Short Term Investments

Short-Term Investments

Restricted Cash

Accounts Receivable

Concentration of Credit Risk

The following table summarizes customers who accounted for 10% or more of net accounts receivable:

	December 31,
	2018			2017
Byram Healthcare		15.5	%		17.2	%
CCS Medical, Inc.		10.1	%		16.2	%
Edgepark Medical Supplies, Inc.	N/A				17.7	%

The following table summarizes customers who accounted for 10% or more of sales for the periods presented:

	Year Ended December 31,
	2018			2017			2016
Edgepark Medical Supplies, Inc.		19.4	%		21.5	%		18.7	%
Byram Healthcare		15.6	%		14.0	%		14.0	%
Solara Medical Supplies, Inc.	N/A			N/A				10.7	%
CCS Medical	N/A				10.3	%	N/A

Fair Value of Financial Instruments

Valuation of Inventory

Long Lived Assets

Property and Equipment

Patents

Deferred Rent

Research and Development Costs

Income Taxes

Revenue Recognition

Trade-In Rights

Revenue Recognition for Arrangements with Multiple Deliverables

Product Returns

Warranty Reserve

	December 31,
(in thousands)	2018			2017
Balance at beginning of the year	$	5,640		$	5,690
Provision for warranties issued during the period		9,617			5,613
Settlements made during the period		(7,797	)		(6,742	)
Increases in warranty estimates		1,678			1,079
Balance at end of the year	$	9,138		$	5,640

Current portion	$	4,206		$	2,596
Non-current portion		4,932			3,044
Total	$	9,138		$	5,640

Stock-Based Compensation

Warrant Liabilities

Advertising Costs

The Company expenses advertising costs as they are incurred. For the years ended December 31, 2018, 2017 and 2016, advertising costs were $0.9 million, $1.1 million, and $0.9 million, respectively.

Shipping and Handling Expenses

Shipping and handling expenses associated with product delivery are included within cost of sales in the Company’s statements of operations.

Comprehensive Loss

Net Loss Per Share

	Year Ended December 31,
	2018		2017		2016
Warrants for common stock		705		—		—
Common stock options		3,477		—		151
ESPP		4		—		2
		4,186		—		153

Accounting Pronouncements Issued and Not Yet Adopted

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Summary of Customers Accounted for 10% or More

The following table summarizes customers who accounted for 10% or more of net accounts receivable:

	December 31,
	2018			2017
Byram Healthcare		15.5	%		17.2	%
CCS Medical, Inc.		10.1	%		16.2	%
Edgepark Medical Supplies, Inc.	N/A				17.7	%

The following table summarizes customers who accounted for 10% or more of sales for the periods presented:

	Year Ended December 31,
	2018			2017			2016
Edgepark Medical Supplies, Inc.		19.4	%		21.5	%		18.7	%
Byram Healthcare		15.6	%		14.0	%		14.0	%
Solara Medical Supplies, Inc.	N/A			N/A				10.7	%
CCS Medical	N/A				10.3	%	N/A

Summary of Reconciliation of Change in Estimated Warranty Liabilities

The following table provides a reconciliation of the change in estimated warranty liabilities for the years ended December 31, 2018 and 2017:

	December 31,
(in thousands)	2018			2017
Balance at beginning of the year	$	5,640		$	5,690
Provision for warranties issued during the period		9,617			5,613
Settlements made during the period		(7,797	)		(6,742	)
Increases in warranty estimates		1,678			1,079
Balance at end of the year	$	9,138		$	5,640

Current portion	$	4,206		$	2,596
Non-current portion		4,932			3,044
Total	$	9,138		$	5,640

Schedule of Anti-Dilutive Securities

	Year Ended December 31,
	2018		2017		2016
Warrants for common stock		705		—		—
Common stock options		3,477		—		151
ESPP		4		—		2
		4,186		—		153

Financial Statement Information (Tables)

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Summary of Estimated Fair Value of Short-Term Investments

The following represents a summary of the estimated fair value of short-term investments at December 31, 2018 and 2017 (in thousands):

At December 31, 2018	Maturity (in years)	Amortized Cost		Unrealized Gain		Unrealized Loss			Estimated Fair Value
Available-for-sale investment securities
Commercial paper	Less than 1	$	53,559	$	—	$	(22	)	$	53,537
U.S. Treasury securities	Less than 1		17,937		—		(2	)		17,935
Corporate debt securities	Less than 1		15,718		12		(1	)		15,729
Total		$	87,214	$	12	$	(25	)	$	87,201

At December 31, 2017	Maturity (in years)	Amortized Cost		Unrealized Gain		Unrealized Loss		Estimated Fair Value
Trading securities:
Mutual funds held for nonqualified deferred compensation plan participants		$	459	$	20	$	—	$	479
Total		$	459	$	20	$	—	$	479

Summary of Accounts Receivable

Accounts receivable consisted of the following (in thousands):

	December 31,
	2018			2017
Accounts receivable	$	37,030		$	22,071
Less allowance for doubtful accounts, and product returns		(1,837	)		(1,278	)
Total	$	35,193		$	20,793

Reconciliation of Change in Estimated Allowance for Doubtful Accounts

The following table provides a reconciliation of the change in estimated allowance for doubtful accounts for the years ended December 31, 2018, 2017 and 2016 (in thousands):

	Allowance for Doubtful Accounts
Balance at December 31, 2015	$	221
Provision for doubtful accounts		632
Write-offs and adjustments, net of recoveries		(118	)
Balance at December 31, 2016	$	735
Provision for doubtful accounts	824
Write-offs and adjustments, net of recoveries		(524	)
Balance at December 31, 2017	$	1,035
Provision for doubtful accounts		1,448
Write-offs and adjustments, net of recoveries		(646	)
Balance at December 31, 2018	$	1,837

Summary of Inventory

Inventory consisted of the following at (in thousands):

	December 31,
	2018		2017
Raw materials	$	6,622	$	10,328
Work-in-process		2,710		3,812
Finished goods		10,564		12,853
Total	$	19,896	$	26,993

Summary of Property and Equipment

Property and equipment consisted of the following at (in thousands):

	December 31,
	2018			2017
Leasehold improvements	$	11,313		$	13,924
Computer equipment and software		8,745			9,040
Office furniture and equipment		4,415			4,686
Manufacturing and scientific equipment		18,306			17,505
		42,779			45,155
Less accumulated depreciation and amortization		(25,628	)		(25,524	)
Total	$	17,151		$	19,631

Summary of Capitalized Patents

The following represents the capitalized patents at December 31, 2018 and 2017 (in thousands)

	December 31,
	2018			2017
Gross amount	$	3,247		$	3,247
Accumulated amortization		(2,117	)		(1,790	)
Total	$	1,130		$	1,457
Weighted average remaining amortization period (in months)		42			54

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis

			Fair Value Measurements at
			December 31, 2018
	December 31, 2018		Level 1		Level 2		Level 3
Assets
Cash equivalents⁽¹⁾	$	37,373	$	37,373	$	—	$	—
Commercial paper		53,537		—		53,537		—
U.S. Treasury securities		17,935		17,935		—		—
Corporate debt securities		15,729				15,729		—
Total assets	$	124,574	$	55,308	$	69,266	$	—
Liabilities
Common stock warrants	$	17,926	$	—	$	—	$	17,926
Total liabilities	$	17,926	$	—	$	—	$	17,926

			Fair Value Measurements at
			December 31, 2017
	December 31, 2017		Level 1		Level 2		Level 3
Assets
Cash equivalents ⁽¹⁾	$	23,700	$	23,700	$	—	$	—
Mutual funds held for nonqualified deferred compensation plan participants⁽²⁾		479		479		—		—
Total assets	$	24,179	$	24,179	$	—	$	—
Liabilities
Common stock warrants	$	5,432	$	—	$	—	$	5,432
Deferred compensation ⁽²⁾		479	$	479	$	—	$	—
Total liabilities	$	5,911	$	479	$	—	$	5,432

(1)

(2)

Schedule of Assumptions Used to Estimate Fair Values of Common Stock Warrants

The assumptions used to estimate the fair values of the common stock warrants at December 31, 2018 and 2017 are presented below:

	Series A Warrants
	December 31, 2018			December 31, 2017
Risk-free interest rate		3.0	%		2.2	%
Expected dividend yield		0.0	%		0.0	%
Expected volatility		78.3	%		63.5	%
Expected term (in years)		3.8			4.8

	Series B Warrants
	December 31, 2018			December 31, 2017
Risk-free interest rate	N/A				1.4	%
Expected dividend yield	N/A				0.0	%
Expected volatility	N/A				80.3	%
Expected term (in years)	N/A				0.3

Summary of Changes in Fair Value of Total Level 3 Financial Assets

The following table presents a summary of changes in fair value of the Company’s total Level 3 financial assets for the years ended December 31, 2018 and 2017:

	2018			2017
Balance at beginning of period	$	5,432		$	6,453
Increase (decrease) in fair value included in change in fair value of common stock warrants		66,494			(1,021	)
Decrease in fair value from warrants exercised during the period		(54,000	)		—
Balance at end of period	$	17,926		$	5,432

Stockholders' Equity (Deficit) (Tables)

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

Summary of Stock Option Activities for 2006 Plan and 2013 Plan

The following table summarizes stock option activities for the 2006 Plan and 2013 Plan:

	Total Options			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2016		822,265		$	84.05		7.92	$	1,593
Granted		615,067		$	4.69
Exercised		(24,406	)	$	11.06			$	338
Canceled/forfeited/expired		(81,657	)	$	110.21
Outstanding at December 31, 2017		1,331,269		$	47.11		8.08	$	—
Granted		4,730,956		$	20.34
Exercised		(136,042	)	$	7.55			$	3,953
Canceled/forfeited/expired		(162,991	)	$	45.46			$	1,466
Outstanding at December 31, 2018		5,763,192		$	23.61		8.94	$	116,988
Vested and expected to vest at December 31, 2018		5,643,473		$	23.73		8.94	$	114,547
Exercisable at December 31, 2018		1,215,287		$	43.40		7.34	$	25,852

Summary of Compensation Cost Included in Consolidated Statement of Operations

The compensation cost that has been included in the consolidated statement of operations for all stock-based compensation arrangements was as follows (in thousands):

	Year Ended December 31,
	2018		2017		2016
Cost of sales	$	2,581	$	1,360	$	1,016
Selling, general & administrative		16,824		10,020		9,360
Research and development		4,331		1,248		1,284
Total	$	23,736	$	12,628	$	11,660

Schedule of Assumptions Used in Black-Scholes Option-Pricing Model

The assumptions used in the Black-Scholes option-pricing model are as follows:

	Stock Option
	Year Ended December 31,
	2018			2017			2016
Weighted average grant date fair value (per share)	$	12.94		$	2.65		$	24.30
Risk-free interest rate		2.8	%		2.1	%		1.7	%
Expected dividend yield		0.0	%		0.0	%		0.0	%
Expected volatility		71.4	%		60.8	%		57.5	%
Expected term (in years)		5.7			5.8			5.8

	ESPP
	Year Ended December 31,
	2018			2017⁽¹⁾
Weighted average grant date fair value (per share)	$	13.48		N/A
Risk-free interest rate		2.5	%	N/A
Expected dividend yield		0.0	%	N/A
Expected volatility		81.2	%	N/A
Expected term (in years)		1.25		N/A

Schedule of Shares of Common Stock Reserved for Future Issuance

The following shares of common stock were reserved for future issuance at December 31, 2018 (in thousands):

Common stock warrants outstanding			804
Stock options issued and outstanding			5,769
Authorized for future option grants			969
Employee stock purchase plan			2,021
			9,563

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense (Benefit)

The expense (benefit) for income taxes reconciles to the amount computed by applying the federal statutory rate to income before taxes as follows (in thousands):

	Year Ended December 31,⁽¹⁾
	2018			2017			2016
Income tax benefit at federal statutory rate	$	(25,738	)	$	(24,829	)	$	(28,362	)
State income tax, net of federal benefit		(1,649	)		(2,034	)		(2,393	)
Warrants revaluation		13,964			(347	)		—
Research and development credits		(1,425	)		(480	)		(720	)
Stock-based compensation		1,362			3,214			1,686
Tax Cuts and Jobs Acts		—			51,577			—
Other		681			138			456
Change in valuation allowance		12,856			(27,231	)		29,318
Income tax expense (benefit)	$	51		$	8		$	(15	)

(1)

For the year ended December 31, 2018 as a result of the Tax Cuts and Jobs Act, the statutory rate was 21%. For the years ended December 31, 2017 and 2016, the statutory rate was 34%.

Schedule of Deferred Tax Assets and Liabilities

	December 31,
	2018			2017
Deferred tax assets:
Net operating loss (NOL) carryforwards	$	85,761		$	81,483
Research and development tax credits carryforwards		4,942			3,517
Capitalized research and development expenses		10,759			12,746
Accrued compensation		13,816			8,809
Other		8,238			4,139
Total deferred tax assets		123,516			110,694
Less valuation allowance		(123,516	)		(110,694	)
Net deferred tax assets	$	—		$	—

Schedule of Unrecognized Tax Benefits

The following table summarizes the activity related to the Company’s gross unrecognized tax benefits at the beginning and end of the years ended December 31, 2018, 2017 and 2016 (in thousands):

	Year Ended December 31,
	2018		2017			2016
Gross unrecognized tax benefits at the beginning of the year	$	8,121	$	8,167		$	7,594
Increases related to current year positions		644		411			580
Increases (decreases) related to prior year positions		59		(457	)		(7	)
Gross unrecognized tax benefits at the end of the year	$	8,824	$	8,121		$	8,167

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Payments Under Noncancelable Operating Leases

Future minimum payments under the aforementioned noncancelable operating leases for each of the five succeeding years following December 31, 2018 are as follows (in thousands):

2019	$	2,743
2020		2,858
2021		2,944
2022		1,644
2023		642
Thereafter		—
	$	10,831

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Information

	For the Quarter Ending
	March 31			June 30			September 30			December 31
2018:
Revenue	$	27,277		$	34,126		$	46,264		$	76,199
Gross profit	$	11,404		$	15,087		$	21,796		$	41,535
Operating expenses	$	26,889		$	29,084		$	37,505		$	40,975
Operating income (loss)	$	(15,485	)	$	(13,997	)	$	(15,709	)	$	560
Net income (loss)	$	(32,693	)	$	(59,359	)	$	(34,245	)	$	3,686
Basic net income (loss) per share ⁽¹⁾	$	(1.82	)	$	(1.17	)	$	(0.62	)	$	0.06
Diluted net income (loss) per share ⁽¹⁾	$	(1.82	)	$	(1.17	)	$	(0.62	)	$	0.02

2017:
Revenue	$	18,977		$	21,327		$	27,003		$	40,294
Gross profit	$	6,753		$	8,001		$	11,873		$	17,468
Operating expenses	$	27,979		$	26,970		$	25,039		$	27,050
Operating loss	$	(21,226	)	$	(18,969	)	$	(13,166	)	$	(9,583	)
Net loss	$	(23,792	)	$	(21,801	)	$	(16,034	)	$	(11,406	)
Basic and diluted net loss per share ⁽¹⁾	$	(7.46	)	$	(4.36	)	$	(3.09	)	$	(1.23	)

(1)

Organization and Basis of Presentation - Additional Information (Detail) $ in Thousands		12 Months Ended
	Oct. 09, 2017	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Organization And Basis Of Presentation [Line Items]
Operating losses and accumulated deficit		$ (600,075)	$ (477,613)
Cash cash equivalents and short term investments		$ 129,000
Reverse stock split of company's issued and outstanding shares of common stock description		1-for-10 reverse stock split
Reverse stock split, conversion ratio	0.1
Insulin Pump [Member] \| Minimum [Member]
Organization And Basis Of Presentation [Line Items]
Expected life span term		4 years
T:slim X2 [Member]
Organization And Basis Of Presentation [Line Items]
Percentage of new pump shipments represented by product hardware platform		100.00%

Summary of Significant Accounting Policies - Additional Information (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($)	Dec. 31, 2018 USD ($) Segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)	Jan. 01, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments \| Segment		1
Guarantee liabilities recognized as sales	$ 1,100,000
Company amortizes patent costs over their estimated useful life		42 months	54 months
Guarantee liabilities in other current liabilities		$ 0	$ 0
Offered period for sales return		30 days
Allowance for product returns		$ 300,000	200,000
Warranty reserve		9,138,000	5,640,000	$ 5,690,000
Advertising cost		900,000	1,100,000	$ 900,000
Subsequent Event [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating lease right-of-use leased assets					$ 12,000,000
Operating lease, liability					12,000,000
Other Current Liabilities [Member] \| Subsequent Event [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred rent					1,000,000
Deferred Rent Long-term [Member] \| Subsequent Event [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred rent					$ 3,800,000
Warranty reserves [Member]
Summary Of Significant Accounting Policies [Line Items]
Warranty reserve		$ 9,100,000	5,600,000
Complementary products [Member]
Summary Of Significant Accounting Policies [Line Items]
Revenue performance obligations satisfied over period		4 years
Deferred revenue		$ 3,800,000	2,000,000
Tandem Pump [Member]
Summary Of Significant Accounting Policies [Line Items]
Warranty period offered		4 years
Slim cartridges and infusion sets [Member]
Summary Of Significant Accounting Policies [Line Items]
Warranty period offered		6 months
Trade-in rights reserve [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred revenue		$ 0	65,000
ASU 2014-09: Revenue from Contracts with Customers [Member]
Summary Of Significant Accounting Policies [Line Items]
Net reduction to accumulated deficit						$ 149,000
Patents [Member]
Summary Of Significant Accounting Policies [Line Items]
Company amortizes patent costs over their estimated useful life		10 years
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets		3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets		7 years
Term Loan Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash		$ 0	$ 10,000,000

Summary of Significant Accounting Policies - Summary of Customers Accounted for 10% or More (Detail) - Customer Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts Receivable [Member] \| Byram Healthcare [Member]
Concentration Risk [Line Items]
Customers accounted for 10% or more	15.50%	17.20%
Accounts Receivable [Member] \| Edgepark Medical Supplies, Inc. [Member]
Concentration Risk [Line Items]
Customers accounted for 10% or more		17.70%
Accounts Receivable [Member] \| CCS Medical, Inc. [Member]
Concentration Risk [Line Items]
Customers accounted for 10% or more	10.10%	16.20%
Sales Revenue Net [Member] \| Byram Healthcare [Member]
Concentration Risk [Line Items]
Customers accounted for 10% or more	15.60%	14.00%	14.00%
Sales Revenue Net [Member] \| Edgepark Medical Supplies, Inc. [Member]
Concentration Risk [Line Items]
Customers accounted for 10% or more	19.40%	21.50%	18.70%
Sales Revenue Net [Member] \| CCS Medical, Inc. [Member]
Concentration Risk [Line Items]
Customers accounted for 10% or more		10.30%
Sales Revenue Net [Member] \| Solara Medical Supplies, Inc.
Concentration Risk [Line Items]
Customers accounted for 10% or more			10.70%

Summary of Significant Accounting Policies - Summary of Reconciliation of Change in Estimated Warranty Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Movement In Standard And Extended Product Warranty Increase Decrease Roll Forward
Beginning balance	$ 5,640	$ 5,690
Provision for warranties issued during the period	9,617	5,613
Settlements made during the period	(7,797)	(6,742)
Increases in warranty estimates	1,678	1,079
Ending balance	9,138	5,640
Current portion	4,206	2,596
Non-current portion	$ 4,932	$ 3,044

Summary of Significant Accounting Policies - Schedule of Anti-Dilutive Securities (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	4,186	153
Warrants for common stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	705
Common stock options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	3,477	151
ESPP [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	4	2

Financial Statement Information - Summary of Estimated Fair Value of Short-Term Investments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Cash Cash Equivalents And Short Term Investments [Line Items]
Short-term investments, Amortized Cost	$ 87,214	$ 459
Short-term investments, Unrealized Gain	12	20
Short-term investments, Unrealized Loss	(25)
Short-term investments, Estimated Fair Value	87,201	479
Commercial paper [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Available-for-sale investment securities, Amortized Cost	53,559
Available-for-sale investment securities, Unrealized Loss	(22)
Available-for-sale investment securities, Estimated Fair Value	$ 53,537
Commercial paper [Member] \| Maximum [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Available-for-sale investment securities, Maturity (in years)	1 year
U.S. Treasury securities [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Available-for-sale investment securities, Amortized Cost	$ 17,937
Available-for-sale investment securities, Unrealized Loss	(2)
Available-for-sale investment securities, Estimated Fair Value	$ 17,935
U.S. Treasury securities [Member] \| Maximum [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Available-for-sale investment securities, Maturity (in years)	1 year
Corporate Debt Securities [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Available-for-sale investment securities, Amortized Cost	$ 15,718
Available-for-sale investment securities, Unrealized Gain	12
Available-for-sale investment securities, Unrealized Loss	(1)
Available-for-sale investment securities, Estimated Fair Value	$ 15,729
Corporate Debt Securities [Member] \| Maximum [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Available-for-sale investment securities, Maturity (in years)	1 year
Trading securities — mutual funds held for nonqualified deferred compensation plan participants [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Trading securities, Amortized Cost		459
Trading securities, Unrealized Gain		20
Trading securities, Estimated Fair Value		$ 479

Financial Statement Information - Summary of Accounts receivable (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts Receivable Net [Abstract]
Accounts receivable	$ 37,030	$ 22,071
Less allowance for doubtful accounts, and product returns	(1,837)	(1,278)
Total	$ 35,193	$ 20,793

Financial Statement Information - Reconciliation of Change in Estimated Allowance for Doubtful Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts
Beginning Balance	$ 1,035	$ 735	$ 221
Provision for doubtful accounts	1,448	824	632
Write-offs and adjustments, net of recoveries	(646)	(524)	(118)
Ending Balance	$ 1,837	$ 1,035	$ 735

Financial Statement Information - Summary of Inventory (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials	$ 6,622	$ 10,328
Work-in-process	2,710	3,812
Finished goods	10,564	12,853
Total	$ 19,896	$ 26,993

Financial Statement Information - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 42,779	$ 45,155
Less accumulated depreciation and amortization	(25,628)	(25,524)
Total property and equipment, net	17,151	19,631
Leasehold improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	11,313	13,924
Computer equipment and software [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	8,745	9,040
Office furniture and equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,415	4,686
Manufacturing and scientific equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 18,306	$ 17,505

Financial Statement Information - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Balance Sheet Components [Abstract]
Depreciation and amortization expense related to property and equipment	$ 5.5	$ 6.5	$ 5.2
Amortization expense related to intangible assets	0.3	$ 0.3	$ 0.3
Estimated annual amortization for 2019	0.3
Estimated annual amortization for 2020	0.3
Estimated annual amortization for 2021	0.3
Estimated annual amortization for 2022	$ 0.2

Financial Statement Information - Summary of Capitalized Patents (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Indefinite Lived Intangible Assets By Major Class [Line Items]
Weighted average remaining amortization period (in months)	42 months	54 months
Patents [Member]
Indefinite Lived Intangible Assets By Major Class [Line Items]
Gross amount	$ 3,247	$ 3,247
Accumulated amortization	(2,117)	(1,790)
Total	$ 1,130	$ 1,457
Weighted average remaining amortization period (in months)	10 years

Fair Value Measurements - Schedule of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	$ 124,574	$ 24,179
Total liabilities	17,926	5,911
Cash equivalents [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	37,373	23,700
Mutual funds held for nonqualified deferred compensation plan participants [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets		479
Commercial paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	53,537
U.S. Treasury securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	17,935
Corporate Debt Securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	15,729
Warrants for common stock [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total liabilities	17,926	5,432
Deferred compensation [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total liabilities		479
Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	55,308	24,179
Total liabilities		479
Level 1 [Member] \| Cash equivalents [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	37,373	23,700
Level 1 [Member] \| Mutual funds held for nonqualified deferred compensation plan participants [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets		479
Level 1 [Member] \| U.S. Treasury securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	17,935
Level 1 [Member] \| Deferred compensation [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total liabilities		479
Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	69,266
Level 2 [Member] \| Commercial paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	53,537
Level 2 [Member] \| Corporate Debt Securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	15,729
Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total liabilities	17,926	5,432
Level 3 [Member] \| Warrants for common stock [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total liabilities	$ 17,926	$ 5,432

Fair Value Measurements - Schedule of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Restricted cash - long-term	$ 10,000
Cash and cash equivalents	$ 13,700	$ 41,826
Maximum [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents maturity term	3 months

Fair Value Measurements - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Transfer between level 1 and level 2 securities	$ 0	$ 0
Warrants initial value	$ 6,500,000	$ 6,500,000
Series A warrants [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Outstanding warrants	510,785
Series A warrants [Member] \| Secondary Public Offering [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Warrants issue to purchase common stock	4,630,000	4,630,000
Warrants exercise price	$ 3.50	$ 3.50
Public offering period	5 years	5 years
Series B warrants [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Outstanding warrants	0
Series B warrants [Member] \| Secondary Public Offering [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Warrants issue to purchase common stock	4,630,000	4,630,000
Warrants exercise price	$ 3.50	$ 6.5
Public offering period	6 months	6 months

Fair Value Measurements - Schedule of Assumptions Used to Estimate Fair Values of Common Stock Warrants (Detail)	Dec. 31, 2018	Dec. 31, 2017
Series A warrants [Member] \| Risk Free Interest Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Risk-free interest rate	3.0	2.2
Series A warrants [Member] \| Expected Dividend Yield [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Risk-free interest rate	0.0	0.0
Series A warrants [Member] \| Expected Volatility [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Risk-free interest rate	78.3	63.5
Series A warrants [Member] \| Expected Term [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Expected term (in years)	3 years 9 months 18 days	4 years 9 months 18 days
Series B warrants [Member] \| Risk Free Interest Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Risk-free interest rate		1.4
Series B warrants [Member] \| Expected Dividend Yield [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Risk-free interest rate		0.0
Series B warrants [Member] \| Expected Volatility [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Risk-free interest rate		80.3
Series B warrants [Member] \| Expected Term [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Expected term (in years)		3 months 18 days

Fair Value Measurements - Summary of Changes in Fair Value of Total Level 3 Financial Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Balance at beginning of period	$ 5,432	$ 6,453
Increase (decrease) in fair value included in change in fair value of common stock warrants	66,494	(1,021)
Decrease in fair value from warrants exercised during the period	(54,000)
Balance at end of period	$ 17,926	$ 5,432

Term Loan Agreement - Additional Information (Detail) - USD ($)	1 Months Ended		12 Months Ended			27 Months Ended
	Feb. 28, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Aug. 31, 2018	Oct. 01, 2015	Sep. 30, 2015
Debt Instrument [Line Items]
Accrued interest		$ 2,832,000	$ 3,930,000	$ 2,832,000		$ 2,832,000
Debt discount associated with financing fees and debt issuance costs			1,721,000	1,883,000	$ 274,000
Loss on extinguishment of debt			5,313,000
Compounded interest payable								2.00%
Additional amount borrowed				1,657,000	$ 927,000	2,700,000
Term Loan Agreement [Member]
Debt Instrument [Line Items]
Loan outstanding		82,700,000	0	82,700,000		82,700,000	$ 82,700,000
Accrued interest							1,100,000
Associated financing fees							$ 5,000,000
Debt discount associated with financing fees and debt issuance costs		6,200,000
Loss on extinguishment of debt			$ 5,300,000
Interest rate			11.50%						11.50%
Interest payable as cash			9.50%					9.50%
Compounded interest payable			2.00%
Interest-only payments description			Under the Term Loan Agreement, interest was payable at the Company’s option, (i) in cash at a rate of 11.5% per annum, or (ii) at a rate of 9.5% of the 11.5% per annum in cash and 2.0% of the 11.5% per annum or the PIK Loan to be added to the principal of the loan and subject to accruing interest. Interest-only payments were due quarterly on March 31, June 30, September 30 and December 31 of each year of the interest-only payment period, which would have ended on December 31, 2019.
Maturity date for interest-only payment			Dec. 31, 2019
Maturity date for principal balance			Mar. 31, 2020
Term Loan Amendments [Member]
Debt Instrument [Line Items]
Warrants life			10 years
Warrants issue to purchase common stock			193,788
Warrants exercise price			$ 23.50
Present value of the future cash flows			10.00%
Accrued back end financing fee	$ 5,000,000	$ 4,100,000		$ 4,100,000		$ 4,100,000
Term Loan Amendments [Member] \| Other Long Term Liabilities And As Contra-Debt In Notes Payable-Long Term [Member]
Debt Instrument [Line Items]
Prepayment fee percentage	6.00%	5.00%

Stockholders' Equity (Deficit) - Additional Information (Detail) - USD ($)			1 Months Ended	3 Months Ended						12 Months Ended
	Jan. 02, 2018	Jan. 01, 2017	Jun. 30, 2018	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Gross proceeds from secondary public offering				$ 115,000,000	$ 69,000,000	$ 16,200,000			$ 23,100,000
Common stock reserved for future issuance										9,563,000
Common stock shares issued										136,042	24,406
Options outstanding						1,331,269				5,763,192	1,331,269	822,265
Stock-based compensation expenses										$ 23,736,000	$ 12,628,000	$ 11,660,000
Total stock-based compensation capitalized as part of cost of inventory										200,000	200,000
Unamortized compensation expense										$ 45,300,000
Share-based compensation expense remaining weighted average vesting term										1 year 8 months 12 days
Expected dividend yield										0.00%
Selling, general & administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expenses										$ 16,824,000	$ 10,020,000	$ 9,360,000
Non-employees [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for grant						0				0	0
Non-employees [Member] \| Selling, general & administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expenses										$ 0	$ 0
Common stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares issued										136,042	24,406
Vesting period of remaining stock										3 years
Common stock options [Member] \| First Anniversary of Vesting Date [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock vested percentage										25.00%
Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares issued										136,000	24,000	15,000
2006 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance										268,561
2006 Stock Incentive Plan [Member] \| Common stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum term of stock options										10 years
2013 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance										969,445			480,900
Common shares outstanding													4.00%
Increase in common stock reserve for issuance	404,776	124,382
Number of shares of authorized for issuance			5,500,000
2013 Stock Incentive Plan [Member] \| Common stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum term of stock options										10 years
Warrants for common stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares issued										8,603,321	0
Secondary Public Offering [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares offered for public offering				4,035,085	34,500,000	4,630,000			1,850,000
Shares offering price per share				$ 28.50	$ 2.00	$ 3.50			$ 12.50		$ 3.50
Secondary Public Offering [Member] \| Series A warrants [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Warrants issue to purchase common stock						4,630,000				4,630,000	4,630,000
Secondary Public Offering [Member] \| Series B warrants [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Warrants issue to purchase common stock						4,630,000				4,630,000	4,630,000
At The Market Offering Program [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Gross proceeds from secondary public offering							$ 4,300,000
At The Market Offering Program [Member] \| Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares offered for public offering							464,108
At The Market Offering Program [Member] \| Common Stock [Member] \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares offering price per share							$ 5.64
At The Market Offering Program [Member] \| Common Stock [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares offering price per share							$ 10.54
ESPP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in common stock reserve for issuance	31,096	101,194	2,000,000
Maximum percentage that employee can contribute for purchase of common stock										15.00%
Offering Period										2 years
Purchase Period										four six-month
Issuance of common stock available for grant										55,600
Percentage of common stock reserve for issuance to be increased													1.00%
Purchase of common stock under ESPP										80,581	38,929
Common stock reserved for issuance description										The number of shares of common stock reserved for issuance increased on January 1 of each calendar year, from January 1, 2014 through January 1, 2018, by the lesser of (a) one percent (1%) of the number of shares issued and outstanding on the immediately preceding December 31, or (b) such lesser number of shares as determined by the Administrator.
Stock-based compensation expenses								$ 2,400,000
Number of shares available for grant										2,020,626
Expected dividend yield										0.00%
ESPP [Member] \| Date of Offering [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price of common stock on date of purchase										85.00%
ESPP [Member] \| Date of Purchase [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price of common stock on date of purchase										85.00%

Stockholders' Equity (Deficit) - Summary of Stock Option Activities for 2006 Plan and 2013 Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stockholders Equity Note [Abstract]
Options, Outstanding at beginning of period	1,331,269	822,265
Options, Granted	4,730,956	615,067
Options, Exercised	(136,042)	(24,406)
Options, Canceled/forfeited/expired	(162,991)	(81,657)
Options, Outstanding at end of period	5,763,192	1,331,269	822,265
Options, Vested and expected to vest at December 31, 2018	5,643,473
Options, Exercisable at December 31, 2018	1,215,287
Weighted-Average Exercise Price Per Share, Outstanding at beginning of period	$ 47.11	$ 84.05
Weighted-Average Exercise Price Per Share, Granted	20.34	4.69
Weighted-Average Exercise Price Per Share, Exercised	7.55	11.06
Weighted-Average Exercise Price Per Share, Canceled/forfeited/expired	45.46	110.21
Weighted-Average Exercise Price Per Share, Outstanding at end of period	23.61	$ 47.11	$ 84.05
Weighted-Average Exercise Price Per Share, Vested and expected to vest at December 31, 2018	23.73
Weighted-Average Exercise Price Per Share, Exercisable at December 31, 2018	$ 43.40
Weighted-Average Remaining Contractual Life, Outstanding	8 years 11 months 8 days	8 years 29 days	7 years 11 months 1 day
Weighted-Average Remaining Contractual Life, Vested and expected to vest at December 31, 2018	8 years 11 months 8 days
Weighted-Average Remaining Contractual Life, Exercisable at December 31, 2018	7 years 4 months 2 days
Aggregate Intrinsic Value, Outstanding at beginning period	$ 116,988		$ 1,593
Aggregate Intrinsic Value, Exercised	3,953	$ 338
Aggregate Intrinsic Value, Canceled/forfeited/expired	1,466
Aggregate Intrinsic Value, Vested and expected to vest at December 31, 2018	114,547
Aggregate Intrinsic Value, Exercisable at December 31, 2018	$ 25,852

Stockholders' Equity (Deficit) - Summary of Compensation Cost Included in Consolidated Statement of Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation cost	$ 23,736	$ 12,628	$ 11,660
Cost of sales [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation cost	2,581	1,360	1,016
Selling, general & administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation cost	16,824	10,020	9,360
Research and development [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation cost	$ 4,331	$ 1,248	$ 1,284

Stockholders' Equity (Deficit) - Schedule of Assumptions Used in Black-Scholes Option-Pricing Model (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield	0.00%
Employee Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average grant date fair value (per share)	$ 12.94	$ 2.65	$ 24.30
Risk-free interest rate	2.80%	2.10%	1.70%
Expected dividend yield	0.00%	0.00%	0.00%
Expected volatility	71.40%	60.80%	57.50%
Expected term (in years)	5 years 8 months 12 days	5 years 9 months 18 days	5 years 9 months 18 days
ESPP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average grant date fair value (per share)	$ 13.48
Risk-free interest rate	2.50%
Expected dividend yield	0.00%
Expected volatility	81.20%
Expected term (in years)	1 year 3 months

Stockholders' Equity (Deficit) - Schedule of Assumptions Used in Black-Scholes Option-Pricing Model (Parenthetical) (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grants made during period	4,730,956	615,067
ESPP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grants made during period		0

Stockholders' Equity (Deficit) - Schedule of Shares of Common Stock Reserved for Future Issuance (Detail) shares in Thousands	Dec. 31, 2018 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	9,563
Warrants for common stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	804
Stock options issued and outstanding [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	5,769
Authorized for future option grants [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	969
Employee stock purchase plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	2,021

Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income tax benefit at federal statutory rate	$ (25,738)	$ (24,829)	$ (28,362)
State income tax, net of federal benefit	(1,649)	(2,034)	(2,393)
Warrants revaluation	13,964	(347)
Research and development credits	(1,425)	(480)	(720)
Stock-based compensation	1,362	3,214	1,686
Tax Cuts and Jobs Acts		51,577
Other	681	138	456
Change in valuation allowance	12,856	(27,231)	29,318
Income tax expense (benefit)	$ 51	$ 8	$ (15)

Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
U.S. federal statutory tax rate	21.00%	34.00%	34.00%

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss (NOL) carryforwards	$ 85,761	$ 81,483
Research and development tax credits carryforwards	4,942	3,517
Capitalized research and development expenses	10,759	12,746
Accrued compensation	13,816	8,809
Other	8,238	4,139
Total deferred tax assets	123,516	110,694
Less valuation allowance	$ (123,516)	$ (110,694)

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Line Items]
Accumulated federal NOL carryforwards	$ 352,700,000
Accumulated state NOL carryforwards	313,500,000
Accumulated state NOL carryforwards	$ 1,100,000
Deferred Tax Assets Tax Credit Carryforwards Research Expiration Year	2028
Research credit carryforwards	$ 4,942,000	$ 3,517,000
Excess tax benefits for which benefit could not previously be recognized	$ 8,824,000	8,121,000	$ 8,167,000	$ 7,594,000
Evaluation of tax position, description	The evaluation of uncertainty in a tax position is a two-step process. The first step involves recognition. The Company determines whether it is more likely than not that a tax position will be sustained upon tax examination, including resolution of any related appeals or litigation, based on only the technical merits of the position. The technical merits of a tax position are derived from both statutory and judicial authority (legislation and statutes, legislative intent, regulations, rulings, and case law) and their applicability to the facts and circumstances of the tax position. If a tax position does not meet the more-likely-than-not recognition threshold, the benefit of that position is not recognized in the financial statements. The second step is measurement. A tax position that meets the more-likely-than-not recognition threshold is measured to determine the amount of benefit to recognize in the financial statements. The tax position is measured as the largest amount of benefit that is greater than 50% likely of being realized upon ultimate resolution with a taxing authority.
Unrecognized tax benefits	$ 7,300,000
Accrual interest and penalties	0	$ 0
Loss before income taxes,domestic	(122,000,000)
Loss before income taxes, foreign	$ (1,000,000)
U.S. federal statutory tax rate	21.00%	34.00%	34.00%
Tax cuts and jobs act of 2017, change in tax rate, deferred tax asset	$ 51,600,000
Tax cuts and jobs cut act of 2017, change in tax rate, decrease in valuation allowance	51,600,000
Tax cuts and jobs act of 2017, change in tax rate, net tax expense	0
Maximum deductions on compensation for certain employees as per 2017 tax act	$ 1,000,000
Minimum [Member]
Income Tax Disclosure [Line Items]
Income tax Realization	50.00%
Maximum [Member]
Income Tax Disclosure [Line Items]
U.S. federal statutory tax rate		35.00%
ASU 2016-09 [Member]
Income Tax Disclosure [Line Items]
Excess tax benefits for which benefit could not previously be recognized	$ 1,800,000
California [Member]
Income Tax Disclosure [Line Items]
Remaining NOL carry forwards amount	$ 183,900,000
NOL carry forwards expiration year	2028
Federal [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforward, expiration date	2026
Research credit carryforwards	$ 5,700,000
State and Local [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforward, expiration date	2019
Foreign [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforward, expiration date	2038
California [Member]
Income Tax Disclosure [Line Items]
Research credit carryforwards	$ 6,300,000

Income Taxes - Schedule of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Gross unrecognized tax benefits at the beginning of the year	$ 8,121	$ 8,167	$ 7,594
Increases related to current year positions	644	411	580
Increases (decreases) related to prior year positions	59	(457)	(7)
Gross unrecognized tax benefits at the end of the year	$ 8,824	$ 8,121	$ 8,167

Collaborations - Additional Information (Detail) - DexCom Agreement [Member] $ in Millions	12 Months Ended		36 Months Ended
	Dec. 31, 2018 USD ($) $ / IntegratedSystem	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Licensing fees paid			$ 3.0
Commit for incremental marketing activities \| $ / IntegratedSystem	100
Marketing fund commitment amount	$ 0.1	$ 1.1

Employee-Benefits - Additional Information (Detail)	12 Months Ended
Employee-Benefits - Additional Information (Detail)	Dec. 31, 2018
Defined Contribution Pension And Other Postretirement Plans Disclosure [Abstract]
Minimum age of employees for defined contribution plan	18 years

Commitments and Contingencies - Additional Information (Detail)		12 Months Ended
	Jun. 30, 2016 Lease	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Noncancelable Operating Lease Agreement Amended Due on May 2019 [Member]
Operating Leased Assets [Line Items]
Lease agreement expiration period		2018-01
Amended lease expiration period		2022-05
Right to terminate description		The Company has the right to terminate the lease on the remaining buildings effective May 31, 2021 upon (i) delivery of written notice to the landlord no later than June 1, 2020, and (ii) an early termination payment to the landlord of approximately $0.4 million.
Early termination payment		$ 400,000
Unsecured standby letter of credit		$ 300,000
Lease agreement expiration period		Jul. 15, 2022
Barnes Canyon Lease Due on November 2023 [Member]
Operating Leased Assets [Line Items]
Lease agreement expiration period	2023-11
Lease term description		The Barnes Canyon Lease is scheduled to expire in November 2023. The Company will also have a one-time option to extend the term of the lease for a period of not less than 36 months and not greater than 60 months, by delivering notice to the landlord at least nine months and not more than 12 months prior to the expiration of the lease.
Number of option to extend lease term \| Lease	1
Interest accrual rate on amounts utilized from tenant improvement allowance			8.00%
Non structural improvements costs			$ 3,900,000	$ 1,000,000
Funded by landlord			2,600,000	700,000
Tl Rent 2017		$ 400,000
Tl Rent 2018		700,000
Tl Rent 2019		700,000
Tl Rent 2020		700,000
Tl Rent 2021		700,000
Tl Rent 2022		700,000
Tl Rent 2023		700,000
Barnes Canyon Lease Due on November 2023 [Member] \| Minimum [Member]
Operating Leased Assets [Line Items]
Period of extended lease term	36 months
Notice period for extend lease term to landlord	9 months
Barnes Canyon Lease Due on November 2023 [Member] \| Maximum [Member]
Operating Leased Assets [Line Items]
Period of extended lease term	60 months
Notice period for extend lease term to landlord	12 months
Tenant improvement allowances received under operating lease			3,400,000
Existing Operating Lease and Barnes Canyon Lease [Member]
Operating Leased Assets [Line Items]
Deferred rent arising from rent escalations and lease incentives		4,800,000	5,600,000
Rent expense		$ 2,600,000	$ 3,500,000	$ 3,100,000

Commitments and Contingencies - Schedule of Future Minimum Payments Under Noncancelable Operating Leases (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019	$ 2,743
2020	2,858
2021	2,944
2022	1,644
2023	642
Total	$ 10,831

Selected Quarterly Financial Data (Unaudited) (Detail) - USD ($)
$ / shares in Units, $ in Thousands

3 Months Ended

12 Months Ended

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2017

Sep. 30, 2017

Jun. 30, 2017

Mar. 31, 2017

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Quarterly Financial Information Disclosure [Abstract]

Revenue

$ 76,199

$ 46,264

$ 34,126

$ 27,277

$ 40,294

$ 27,003

$ 21,327

$ 18,977

$ 183,866

$ 107,601

$ 84,248

Gross profit

41,535

21,796

15,087

11,404

17,468

11,873

8,001

6,753

89,822

44,094

23,592

Operating expenses

40,975

37,505

29,084

26,889

27,050

25,039

26,970

27,979

134,453

107,038

101,643

Operating income (loss)

560

(15,709)

(13,997)

(15,485)

(9,583)

(13,166)

(18,969)

(21,226)

(44,631)

(62,944)

(78,051)

Net loss

$ 3,686

$ (34,245)

$ (59,359)

$ (32,693)

$ (11,406)

$ (16,034)

$ (21,801)

$ (23,792)

$ (122,611)

$ (73,033)

$ (83,447)

Basic net income (loss) per share

^[1]

$ 0.06

$ (0.62)

$ (1.17)

$ (1.82)

Diluted net income (loss) per share

^[1]

$ 0.02

$ (0.62)

$ (1.17)

$ (1.82)

Basic and diluted net loss per share

$ (1.23)

^[1]

$ (3.09)

^[1]

$ (4.36)

^[1]

$ (7.46)

^[1]

$ (2.55)

$ (12.87)

$ (27.30)

[1]	Net income (loss) per share is computed independently for each quarter and the full year based upon the respective average shares outstanding in each period. Therefore, the sum of the quarterly per-share calculations may not equal the reported annual per share amounts.

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

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+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References

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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Subsequent Event - Additional Information (Detail) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2019 USD ($) ft²	Dec. 31, 2018 USD ($)
Subsequent Event [Line Items]
Future minimum payments under lease including reimbursement of certain landlord operating expenses		$ 10,831
10935 Vista Sorrento Parkway, San Diego, California [Member]
Subsequent Event [Line Items]
Lease term description		Subject to limited exceptions, the initial lease term is expected to commence on the later of (i) March 1, 2019, or (ii) the date on which the landlord substantially completes certain specified work related to tenant improvements, such date the Commencement Date, and will expire 42 months from the first day of the first full month following the Commencement Date.
Subsequent Event [Member] \| 10935 Vista Sorrento Parkway, San Diego, California [Member]
Subsequent Event [Line Items]
General administrative office space leased \| ft²	25,332
Operating lease maturity period	42 months
Period of extended lease term	5 years
Future minimum payments under lease including reimbursement of certain landlord operating expenses	$ 3,500