Inogen (INGN) 10-K 26 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2018	Feb. 22, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	INGN
Entity Registrant Name	Inogen Inc
Entity Central Index Key	1,294,133
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 Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		21,814,895
Entity Public Float			$ 1.2

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 196,634	$ 142,953
Marketable securities	43,715	30,991
Accounts receivable, net	37,041	31,444
Inventories, net	27,071	18,842
Deferred cost of revenue	359	361
Income tax receivable	2,655	1,313
Prepaid expenses and other current assets	7,108	2,584
Total current assets	314,583	228,488
Property and equipment
Rental equipment, net	43,038	49,349
Manufacturing equipment and tooling	7,338	6,858
Computer equipment and software	6,153	5,484
Furniture and equipment	1,445	746
Leasehold improvements	3,407	1,598
Land and building	125	125
Construction in process	3,128	408
Total property and equipment	64,634	64,568
Less accumulated depreciation	(42,293)	(44,465)
Property and equipment, net	22,341	20,103
Goodwill	2,257	2,363
Intangible assets, net	3,755	4,717
Deferred tax asset - noncurrent	30,130	18,636
Other assets	2,832	765
Total assets	375,898	275,072
Current liabilities
Accounts payable and accrued expenses	26,786	20,626
Accrued payroll	11,407	6,877
Warranty reserve - current	3,549	2,505
Deferred revenue - current	4,451	3,533
Income tax payable	392	345
Total current liabilities	46,585	33,886
Long-term liabilities
Warranty reserve - noncurrent	5,981	3,666
Deferred revenue - noncurrent	11,844	9,402
Deferred tax liability - noncurrent	232	348
Other noncurrent liabilities	832	729
Total liabilities	65,474	48,031
Commitments and contingencies (Note 7)
Stockholders' equity
Common stock, $0.001 par value per share; 200,000,000 shares authorized; 21,778,632 and 20,976,350 shares issued and outstanding as of December 31, 2018 and 2017, respectively	22	21
Additional paid-in capital	249,194	218,109
Retained earnings	60,484	8,639
Accumulated other comprehensive income	724	272
Total stockholders' equity	310,424	227,041
Total liabilities and stockholders' equity	$ 375,898	$ 275,072

Consolidated Balance Sheets (Pa

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	200,000,000
Common stock, shares issued	21,778,632	20,976,350
Common stock, shares outstanding	21,778,632	20,976,350

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue
Sales revenue	$ 336,015	$ 225,492	$ 168,170
Rental revenue	22,096	23,946	34,659
Total revenue	358,111	249,438	202,829
Cost of revenue
Cost of sales revenue	163,989	110,163	85,154
Cost of rental revenue, including depreciation of $7,567, $9,835 and $11,429, respectively	15,542	18,038	20,365
Total cost of revenue	179,531	128,201	105,519
Gross profit
Gross profit-sales revenue	172,026	115,329	83,016
Gross profit-rental revenue	6,554	5,908	14,294
Total gross profit	178,580	121,237	97,310
Operating expense
Research and development	7,029	5,313	5,113
Sales and marketing	95,641	50,758	37,540
General and administrative	38,018	37,576	31,793
Total operating expense	140,688	93,647	74,446
Income from operations	37,892	27,590	22,864
Other income (expense)
Interest expense			(6)
Interest income	3,259	765	196
Other income (expense)	(696)	1,301	(329)
Total other income (expense), net	2,563	2,066	(139)
Income before provision (benefit) for income taxes	40,455	29,656	22,725
Provision (benefit) for income taxes	(11,390)	8,654	2,206
Net income	51,845	21,002	20,519
Other comprehensive income (loss), net of tax
Change in foreign currency translation adjustment	31	363
Change in net unrealized gains (losses) on foreign currency hedging	981	(567)	55
Less: reclassification adjustment for net (gains) losses included in net income	(577)	446	6
Total net change in unrealized gains (losses) on foreign currency hedging	404	(121)	61
Change in net unrealized gains (losses) on marketable securities	17	65	(59)
Total other comprehensive income, net of tax	452	307	2
Comprehensive income	$ 52,297	$ 21,309	$ 20,521
Basic net income per share attributable to common stockholders (Note 2)	$ 2.44	$ 1.02	$ 1.02
Diluted net income per share attributable to common stockholders (Note 2)	$ 2.30	$ 0.96	$ 0.97
Weighted-average number of shares used in calculating net income per share attributable to common stockholders:
Basic common shares	21,266,696	20,683,807	20,067,152
Diluted common shares	22,514,513	21,897,988	21,095,867

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Depreciation	$ 7,567	$ 9,835	$ 11,429

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Retained earnings (accumulated deficit)	Accumulated other comprehensive income (loss)
Beginning Balance at Dec. 31, 2015	$ 134,018	$ 20	$ 179,143	$ (45,108)	$ (37)
Beginning Balance,shares at Dec. 31, 2015		19,782,403
Cumulative effect of change in accounting principle	12,226			12,226
Stock-based compensation	7,294		7,294
Employee stock purchases	1,055		1,055
Employee stock purchases, shares		37,378
Stock options exercised	$ 6,974		6,974
Stock options exercised, shares	570,079	570,079
Net income	$ 20,519			20,519
Other comprehensive income	2				2
Ending Balance at Dec. 31, 2016	182,088	$ 20	194,466	(12,363)	(35)
Ending Balance,shares at Dec. 31, 2016		20,389,860
Stock-based compensation	9,640		9,640
Employee stock purchases	1,379		1,379
Employee stock purchases, shares		24,523
Stock options exercised	$ 12,625	$ 1	12,624
Stock options exercised, shares	520,393	561,967
Net income	$ 21,002			21,002
Other comprehensive income	307				307
Ending Balance at Dec. 31, 2017	227,041	$ 21	218,109	8,639	272
Ending Balance,shares at Dec. 31, 2017		20,976,350
Stock-based compensation	12,790		12,790
Employee stock purchases	2,348		2,348
Employee stock purchases, shares		25,532
Restricted stock awards issued, shares		56,609
Vesting of restricted stock units, shares		18,112
Shares withheld related to net restricted stock settlement	(1,208)		(1,208)
Shares withheld related to net restricted stock settlement, shares		(6,290)
Stock options exercised	$ 17,156	$ 1	17,155
Stock options exercised, shares	708,319	708,319
Net income	$ 51,845			51,845
Other comprehensive income	452				452
Ending Balance at Dec. 31, 2018	$ 310,424	$ 22	$ 249,194	$ 60,484	$ 724
Ending Balance,shares at Dec. 31, 2018		21,778,632

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities
Net income	$ 51,845	$ 21,002	$ 20,519
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	11,295	12,302	13,558
Loss on rental assets and other fixed assets	1,160	1,136	1,202
Gain on sale of former rental assets	(416)	(64)	(272)
Provision for sales returns and doubtful accounts	17,518	13,773	11,082
Provision for rental revenue adjustments	2,678	5,057	10,777
Provision for inventory losses	351	340	133
Stock-based compensation expense	12,790	9,640	7,294
Deferred income taxes	(11,595)	7,947	1,036
Changes in operating assets and liabilities:
Accounts receivable	(25,963)	(18,263)	(32,738)
Inventories	(9,972)	(5,894)	(7,458)
Deferred cost of revenue	2	37	(1)
Income tax receivable	(1,348)	(875)	1,725
Prepaid expenses and other current assets	(4,526)	(819)	(789)
Other noncurrent assets	(1,626)
Accounts payable and accrued expenses	6,360	7,438	(86)
Accrued payroll	4,538	722	852
Warranty reserve	3,359	2,689	1,507
Deferred revenue	3,360	3,654	2,759
Income tax payable	64	225	(11)
Other noncurrent liabilities	103	447	(55)
Net cash provided by operating activities	59,977	60,494	31,034
Cash flows from investing activities
Purchases of marketable securities	(76,162)	(46,933)	(33,142)
Maturities of marketable securities	63,455	37,041	28,843
Investment in intangible assets	(350)	(3,316)	(113)
Investment in property and equipment	(8,043)	(2,914)	(1,718)
Production and purchase of rental equipment	(4,580)	(3,997)	(6,185)
Proceeds from sale of former assets	715	183	388
Payment for acquisition, net of cash acquired		(4,494)
Net cash used in investing activities	(24,965)	(24,430)	(11,927)
Cash flows from financing activities
Proceeds from stock options exercised	17,156	12,625	6,974
Proceeds from employee stock purchases	2,348	1,379	1,055
Payment of employment taxes related to release of restricted stock	(1,208)
Repayment of debt from investment in intangible assets			(315)
Net cash provided by financing activities	18,296	14,004	7,714
Effect of exchange rates on cash	373	34	(76)
Net increase in cash and cash equivalents	53,681	50,102	26,745
Cash and cash equivalents, beginning of period	142,953	92,851	66,106
Cash and cash equivalents, end of period	196,634	142,953	92,851
Supplemental disclosures of cash flow information
Cash paid during the period for interest			10
Cash paid (received) during the period for income taxes, net of refunds received	1,653	1,267	$ (447)
Supplemental disclosures of non-cash transactions
Property and equipment in account payable and accrued expenses	$ 125	$ 70

Nature of Business

Nature of Business	12 Months Ended
	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Business	1. Nature of business Inogen, Inc. (Company or Inogen) was incorporated in Delaware on November 27, 2001. The Company is a medical technology company that primarily develops, manufactures and markets innovative portable oxygen concentrators used to deliver supplemental long-term oxygen therapy to patients suffering from chronic respiratory conditions. Traditionally, these patients have relied on stationary oxygen concentrator systems for use in the home and oxygen tanks or cylinders for mobile use, which the Company calls the delivery model. The tanks and cylinders must be delivered regularly and have a finite amount of oxygen, which requires patients to plan activities outside of their homes around delivery schedules and a finite oxygen supply. Additionally, patients must attach long, cumbersome tubing to their stationary concentrators simply to enable mobility within their homes. The Company’s proprietary Inogen One ® Since adopting the Company’s direct-to-consumer rental strategy in 2009, the Company has directly sold or rented more than 567,000 of its Inogen oxygen concentrators as of December 31, 2018. The Company incorporated Inogen Europe Holding B.V., a Dutch limited liability company, on April 13, 2017. The Company owned all outstanding stock of Inogen Europe Holding B.V., which became a wholly owned subsidiary of the Company. On May 4, 2017, Inogen Europe Holding B.V. acquired all issued and outstanding capital stock of MedSupport Systems B.V. (MedSupport) and began operating under the name Inogen Europe B.V. for approximately $5,831 comprised of $5,779 of cash paid at closing and net working capital adjustments of approximately $52 paid in the fourth quarter of 2017. In aggregate, $1,337 was cash acquired, $1,529 was attributed to intangible assets, $2,154 was attributed to goodwill, and $811 was attributed to net assets assumed. MedSupport is engaged in the business of importing and distributing medical devices throughout Europe. The acquisition allows the Company to add a European customer support and repair site in the Netherlands and is currently operating as Inogen Europe B.V. Goodwill associated with this acquisition is not deductible for tax purposes in the Netherlands. Acquisition expenses of approximately $370 were expensed in 2017 and classified within general and administrative expense. Pro forma results of operations for this acquisition have not been presented because they are not material to the consolidated results of operations. The Company merged Inogen Europe Holding B.V. and Inogen Europe B.V. on December 28, 2018.

Summary of Significant Accounti

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 Basis of presentation The consolidated financial statements of the Company have been prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP). Basis of consolidation The consolidated financial statements include the accounts of Inogen, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated. Accounting estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Management bases these estimates and assumptions upon historical experience, existing and known circumstances, authoritative accounting pronouncements and other factors that management believes to be reasonable. Significant areas requiring the use of management estimates relate to revenue recognition and determining the stand-alone selling price (SSP) of performance obligations, inventory and rental asset valuations and write-downs, accounts receivable allowances for bad debts, returns and adjustments, warranty expense, stock compensation expense, depreciation and amortization, income tax provision and uncertain tax positions, fair value of financial instruments, and fair value of acquired intangible assets and goodwill. Actual results could differ from these estimates. Revenue The Company generates revenue primarily from sales and rentals of its products. The Company’s products consist of its proprietary line of oxygen concentrators and related accessories. Other revenue, which is included in sales revenue on the Statements of Comprehensive Income, primarily comes from service contracts, replacement parts and freight revenue for product shipments. Sales revenue Revenue is recognized upon transfer of control of promised products or services to customers in an amount that reflects the consideration the Company expects to receive in exchange for those products or services. Revenue from product sales is generally recognized upon shipment of the product but is deferred for certain transactions when control has not yet transferred to the customer. The Company’s product is generally sold with a right of return and the Company may provide other incentives, which are accounted for as variable consideration when estimating the amount of revenue to recognize. Returns and incentives are estimated at the time sales revenue is recognized. The provisions for estimated returns are made based on known claims and estimates of additional returns based on historical data and future expectations. Sales revenue incentives within the Company’s contracts are estimated based on the most likely amounts expected on the related sales transaction and recorded as a reduction to revenue at the time of sale in accordance with the terms of the contract. The Company also offers a lifetime warranty for direct-to-consumer sales of its portable oxygen concentrators. For a fixed price, the Company agrees to provide a fully functional portable oxygen concentrator for the remaining life of the patient. Lifetime warranties are only offered to patients upon the initial sale of portable oxygen concentrators directly from the Company and are non-transferable. Lifetime warranties are considered to be a distinct performance obligation that are accounted for separately from its sale of portable oxygen concentrators with a standard warranty of three years . The revenue is allocated to the distinct lifetime warranty performance obligation based on a relative SSP method. The Company has vendor-specific objective evidence of the selling price for its equipment. To determine the selling price of the lifetime warranty, the Company uses its best estimate of the SSP for the distinct performance obligation as the lifetime warranty is neither separately priced nor is the selling price available through third-party evidence. To calculate the selling price associated with the lifetime warranties, management considers the profit margins of service revenue, the average estimated cost of lifetime warranties and the price of extended warranties. Revenue from the distinct lifetime warranty is deferred after the delivery of the equipment and recognized based on an estimated mortality rate over five years, which is the estimated performance period of the contract based on the average patient life expectancy. Revenue from the sale of the Company’s repair services is recognized when the performance obligations are satisfied and collection of the receivables is probable. Other revenue from the sale of replacement parts is generally recognized when product is shipped to customers. Freight revenue consists of fees associated with the deployment of products internationally and domestically when expedited freight options are requested or when minimum order quantities are not met. Freight revenue is generally recognized upon shipment of the product but is deferred if control has not yet transferred to the customer. Shipping and handling costs for sold products and rental assets shipped to the Company’s customers are included on the consolidated statement of comprehensive income as part of cost of sales revenue and cost of rental revenue, respectively. The payment terms and conditions of customer contracts vary by customer type and the products and services offered. For certain products or services and customer types, the Company requires payment before the products or services are delivered to the customer. The timing of sales revenue recognition, billing and cash collection results in billed accounts receivable and deferred revenue in the consolidated balance sheet. Contract liabilities primarily consist of deferred revenue related to lifetime warranties on direct-to-consumer sales revenue when cash payments are received in advance of services performed under the contract. The contract with the customer states the final terms of the sale, including the description, quantity, and price of each product or service purchase. The increase in deferred revenue related to lifetime warranties were primarily driven by $6,909 and $4,290 of payments received in advance of satisfying performance obligations for the years ended December 31, 2018 and December 31, 2017, respectively, par and $752 . $14,874 10,820 The Company elected to apply the practical expedient in accordance with Accounting Standards Codification (ASC) — Revenue Recognition did not evaluate contracts of one year or less for the existence of a significant financing component The Company’s sales revenue is primarily derived from the sale of its Inogen One systems, Inogen At Home systems, and related accessories to individual consumers, home medical equipment providers, distributors, the Company’s private label partner and resellers worldwide. Sales revenue is classified into two areas: business-to-business sales and direct-to-consumer sales. The following table sets forth the Company’s sales revenue disaggregated by sales channel and geographic region: (amounts in thousands) Years ended December 31, Revenue by region and category 2018 2017 2016 Business-to-business domestic sales $ 116,581 $ 83,390 $ 56,605 Business-to-business international sales 77,333 55,519 50,106 Direct-to-consumer domestic sales 142,101 86,583 61,459 Total sales revenue $ 336,015 $ 225,492 $ 168,170 Rental revenue The Company recognizes equipment rental revenue over the non-cancelable lease term, which is one month, less estimated adjustments, in accordance with ASC 840— Leases The lease term begins on the date products are shipped to patients and are recorded at amounts estimated to be received under reimbursement arrangements with third-party payors, including Medicare, private payors, and Medicaid. Due to the nature of the industry and the reimbursement environment in which the Company operates, certain estimates are required to record net revenue and accounts receivable at their net realizable values. Inherent in these estimates is the risk that they will have to be revised or updated as additional information becomes available. Specifically, the complexity of many third-party billing arrangements and the uncertainty of reimbursement amounts for certain services from certain payors may result in adjustments to amounts originally recorded. Such adjustments are typically identified and recorded at the point of cash application, claim denial or account review. The Company adjusts revenue for historical trends on revenue adjustments due to timely filings, deaths, hospice, and other types of analyzable adjustments on a monthly basis. Accounts receivable are reduced by an allowance for doubtful accounts which provides for those accounts from which payment is not expected to be received although product was delivered and revenue was earned. The determination that an account is uncollectable and the ultimate write-off of that account occurs once collection is considered to be highly unlikely, and it is written-off and charged to the allowance at that time. Amounts billed but not earned due to the timing of the billing cycle are deferred and recognized in revenue on a straight-line basis over the monthly billing period. For example, if the first day of the billing period does not fall on the first of the month, then a portion of the monthly billing period will fall in the subsequent month and the related revenue and cost would be deferred based on the service days in the following month. Rental revenue is recognized as earned, less estimated adjustments. Revenue not billed at the end of the period is reviewed for the likelihood of collections and accrued. The rental revenue stream is not guaranteed and payment will cease if the patient no longer needs oxygen or returns the equipment. Revenue recognized is at full estimated allowable amounts; transfers to secondary insurances or patient responsibility have no net effect on revenue. Rental revenue is earned for that entire month if the patient is on service on the first day of the 30-day period commencing on the recurring date of service for a particular claim, regardless if there is a change in condition or death after that date. Included in rental revenue are unbilled amounts for which the revenue recognition criteria had been met as of period-end but were not yet billed to the payor. The estimate of net unbilled rental revenue recognized is based on historical trends and estimates of future collectability. In addition, the Company estimates potential future adjustments and write-offs of these unbilled amounts and includes these estimates in the allowance for adjustments and write-offs of rental revenue which is netted against gross receivables. Fair value of financial instruments The Company’s financial instruments consist of cash and cash equivalents, marketable securities, accounts receivable, accounts payable and accrued expenses. The carrying values of its financial instruments approximate fair value based on their short-term nature. Imputed interest associated with the Company’s non-interest bearing debt was insignificant and was appropriately recognized in the respective periods. Fair value accounting ASC 820 — Fair Value Measurements and Disclosures Level input Input definition Level 1 Inputs are unadjusted, quoted prices for identical assets or liabilities in active markets at the measurement date. Level 2 Inputs, other than quoted prices included in Level 1 that are observable for the asset or liability through corroboration with market data at the measurement date. Level 3 Unobservable inputs that reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. The Company obtained the fair value of its available-for-sale securities, which are not in active markets, from a third-party professional pricing service using quoted market prices for identical or comparable instruments, rather than direct observations of quoted prices in active markets. The Company's professional pricing service gathers observable inputs for all of its fixed income securities from a variety of industry data providers (e.g., large custodial institutions) and other third-party sources. Once the observable inputs are gathered, all data points are considered and the fair value is determined. The Company validates the quoted market prices provided by its primary pricing service by comparing their assessment of the fair values against the fair values provided by its investment managers. The Company's investment managers use similar techniques to its professional pricing service to derive pricing as described above. As all significant inputs were observable, derived from observable information in the marketplace or supported by observable levels at which transactions are executed in the marketplace, the Company has classified its marketable securities within Level 2 of the fair value hierarchy. The following table summarizes fair value measurements by level for the assets measured at fair value on a recurring basis for cash, cash equivalents and marketable securities: As of December 31, 2018 Gross Cash Adjusted unrealized and cash Marketable (amounts in thousands) cost gains (losses) Fair value equivalents securities Cash $ 33,671 $ — $ 33,671 $ 33,671 $ — Level 1: Money market accounts 158,438 — 158,438 158,438 — Level 2: Corporate bonds 13,629 (16 ) 13,613 — 13,613 U.S. Treasury securities 34,620 7 34,627 4,525 30,102 Total $ 240,358 $ (9 ) $ 240,349 $ 196,634 $ 43,715 As of December 31, 2017 Gross Cash Adjusted unrealized and cash Marketable (amounts in thousands) cost losses Fair value equivalents securities Cash $ 46,237 $ — $ 46,237 $ 46,237 $ — Level 1: Money market accounts 93,430 — 93,430 93,430 — Level 2: Certificates of deposit 11,010 (4 ) 11,006 490 10,516 Corporate bonds 20,789 (21 ) 20,768 2,796 17,972 Agency mortgage-backed securities 2,005 (1 ) 2,004 — 2,004 U.S. Treasury securities 499 — 499 — 499 Total $ 173,970 $ (26 ) $ 173,944 $ 142,953 $ 30,991 The following table summarizes the estimated fair value of the Company’s investments in marketable securities, classified by the contractual maturity date of the securities: December 31, (amounts in thousands) 2018 Due within one year $ 43,715 Due in one year through five years — Total $ 43,715 Derivative instruments and hedging activities The Company transacts business in foreign currencies and has international sales and expenses denominated in foreign currencies, subjecting the Company to foreign currency risk. The Company has entered into foreign currency forward contracts, generally with maturities of twelve months or less, to reduce the volatility of cash flows primarily related to forecasted revenue denominated in certain foreign currencies. These contracts allow the Company to sell Euros in exchange for U.S. dollars at specified contract rates. Forward contracts are used to hedge forecasted sales over specific months. Changes in the fair value of these forward contracts designed as cash flow hedges are recorded as a component of accumulated other comprehensive income (loss) income within stockholders’ equity and are recognized in the consolidated statements of comprehensive income during the period which approximates the time the corresponding sales occur. The Company may also enter into foreign exchange contracts that are not designated as hedging instruments for financial accounting purposes. These contracts are generally entered into to offset the gains and losses on certain asset and liability balances until the expected time of repayment. Accordingly, any gains or losses resulting from changes in the fair value of the non-designated contracts are reported in other expense, net in the consolidated statements of comprehensive income. The gains and losses on these contracts generally offset the gains and losses associated with the underlying foreign currency-denominated balances, which are also reported in other income (expense), net. The Company records the assets or liabilities associated with derivative instruments and hedging activities at fair value based on Level 2 inputs in other current assets or other current liabilities, respectively, in the consolidated balance sheet. The Company had a receivable of $472 and a payable of $66 as of December 31, 2018 and 2017, respectively. The Company classifies the foreign currency derivative instruments within Level 2 in the fair value hierarchy as the valuation inputs are based on quoted prices and market observable data of whether it is designated and qualifies for hedge accounting. The Company documents the hedging relationship and its risk management objective and strategy for undertaking the hedge, the hedging instrument, the hedged transaction, the nature of the risk being hedged, how the hedging instrument’s effectiveness in offsetting the hedged risk will be assessed prospectively and retrospectively, and a description of the method used to measure ineffectiveness. The Company assesses hedge effectiveness and ineffectiveness at a minimum quarterly but may assess it monthly. For derivative instruments that are designed and qualify as part of a cash flow hedging relationship, the effective portion of the gain or loss on the derivative is reported in other comprehensive income (loss) and reclassified into earnings in the same periods during which the hedged transaction affects earnings. Gains and losses on the derivative representing either hedge ineffectiveness or hedge components excluded from the assessment of effectiveness are recognized in current period earnings. The Company will discontinue hedge accounting prospectively when it determines that the derivative is no longer effective in offsetting cash flows attributable to the hedge risk. The cash flow hedge is de-designated because a forecasted transaction is not probable of occurring, or management determines to remove the designation of the cash flow hedge. In all situations in which hedge accounting is discontinued and the derivative remains outstanding, the Company continues to carry the derivative at its fair value on the balance sheet and recognizes any subsequent changes in the fair value in earnings. When it is probable that a forecasted transaction will not occur, the Company will discontinue hedge accounting and recognize immediately in earnings gains and losses that were accumulated in other comprehensive income (loss) related to the hedging relationship. Accumulated other comprehensive income (loss) The components of accumulated other comprehensive income (loss) were as follows: As of December 31, 2018 Foreign Unrealized Unrealized Accumulated currency gains (losses) on gains (losses) other translation marketable on cash comprehensive (amounts in thousands) adjustments securities flow hedges income Balance as of December 31, 2017 $ 363 $ (17 ) $ (74 ) $ 272 Other comprehensive gain 31 17 404 452 Balance as of December 31, 2018 $ 394 $ — $ 330 $ 724 As of December 31, 2017 Foreign Unrealized Unrealized Accumulated currency gains (losses) on gains (losses) other translation marketable on cash comprehensive (amounts in thousands) adjustments securities flow hedges income (loss) Balance as of December 31, 2016 $ — $ (82 ) $ 47 $ (35 ) Other comprehensive gain (loss) 363 65 (121 ) 307 Balance as of December 31, 2017 $ 363 $ (17 ) $ (74 ) $ 272 Comprehensive income (loss) is the total net earnings and all other non-owner changes in equity. Except for net income and unrealized gains and losses on cash flow hedges, the Company does not have any transactions or other economic events that qualify as comprehensive income (loss). Cash, cash equivalents, and marketable securities The Company considers all short-term highly liquid investments with a maturity of three months or less to be cash equivalents. The Company’s marketable debt securities have been classified and accounted for as available-for-sale. Cash equivalents are recorded at cost plus accrued interest, which is considered adjusted cost, and approximates fair value. Marketable debt securities are included in cash equivalents and marketable securities based on the maturity date of the security. Short-term investments are included in marketable securities in the current period presentation. The Company considers investments with maturities greater than three months, but less than one year, to be marketable securities. Investments are reported at fair value with realized and unrealized gains or losses reported in other income (expense), net. The Company reviews its investments to identify and evaluate investments that have an indication of possible impairment. Factors considered in determining whether a loss is temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition and near-term prospects of the investee, and the Company's intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in market value. Credit losses and other-than-temporary impairments are declines in fair value that are not expected to recover and are charged to other income (expense), net. Cash, cash equivalents, and marketable securities consist of the following: (amounts in thousands) December 31, Cash and cash equivalents 2018 2017 Cash $ 33,671 $ 46,237 Money market accounts 158,438 93,430 Certificates of deposit — 490 Corporate bonds — 2,796 U.S. Treasury securities 4,525 — Total cash and cash equivalents $ 196,634 $ 142,953 Marketable securities Certificates of deposit $ — $ 10,516 Corporate bonds 13,613 17,972 Agency mortgage-backed securities — 2,004 U. S. Treasury securities 30,102 499 Total marketable securities $ 43,715 $ 30,991 Accounts receivable and allowance for bad debts, returns, and adjustments Accounts receivable are customer obligations due under normal sales and rental terms. The Company performs credit evaluations of the customers’ financial condition and generally does not require collateral. The allowance for doubtful accounts is maintained at a level that, in management’s opinion, is adequate to absorb potential losses related to accounts receivable and is based upon the Company’s continuous evaluation of the collectability of outstanding balances. Management’s evaluation takes into consideration such factors as past bad debt experience, economic conditions and information about specific receivables. The Company’s evaluation also considers the age and composition of the outstanding amounts in determining their net realizable value. The allowance for doubtful accounts is based on estimates, and ultimate losses may vary from current estimates. As adjustments to these estimates become necessary, they are reported in general and administrative expense in the periods in which they become known. This allowance is increased by bad debt provisions charged to bad debt expense, net of recoveries, in operating expense and is reduced by direct write-offs. The Company generally does not allow returns from providers for reasons not covered under its standard warranty. Therefore, provision for returns applies primarily to direct-to-consumer sales. This reserve is calculated based on actual historical return rates under the Company’s 30-day return program and is applied to the related sales revenue for the last month of the quarter reported. The Company also records an allowance for rental revenue adjustments which is recorded as a reduction of rental revenue and net rental accounts receivable balances. These adjustments result from contractual adjustments, audit adjustments, untimely claims filings, or billings not paid due to another provider performing same or similar functions for the patient in the same period, all of which prevent billed revenue from becoming realizable. The reserve is based on historical revenue adjustments as a percentage of rental revenue billed and unbilled during the related period. When recording the allowance for doubtful accounts, the bad debt expense account (general and administrative expense account) is charged; when recording allowance for sales returns, the sales returns account (contra sales revenue account) is charged; and when recording the allowance for rental reserve adjustments, the rental revenue adjustments account (contra rental revenue account) is charged. As of December 31, 2018 and December 31, 2017, included in accounts receivable on the consolidated balance sheets were earned but unbilled receivables of $589 and $1,470, respectively. These balances reflect gross unbilled receivables prior to any allowances for adjustments and write-offs. The Company consistently applies its allowance estimation methodology from period-to-period. The Company’s best estimate is made on an accrual basis and adjusted in future periods as required. Any adjustments to the prior period estimates are included in the current period. As additional information becomes known, the Company adjusts its assumptions accordingly to change its estimate of the allowance. For the years ended December 31, 2018 and December 31, 2017, the Company had increases of $1,757 and $3,442, respectively, in the provision for bad debt and revenue adjustments related to prior years. Gross accounts receivable balance concentrations by major category as of December 31, 2018 and December 31, 2017 were as follows: As of As of (amounts in thousands) December 31, 2018 December 31, 2017 Gross accounts receivable $ % $ % Rental (1) $ 3,406 8.7 % $ 6,236 18.0 % Business-to-business and other receivables (2) 35,656 91.3 % 28,474 82.0 % Total gross accounts receivable $ 39,062 100.0 % $ 34,710 100.0 % Net accounts receivable (gross accounts receivable, net of allowances) balance concentrations by major category as of December 31, 2018 and December 31, 2017 were as follows: As of As of (amounts in thousands) December 31, 2018 December 31, 2017 Net accounts receivable $ % $ % Rental (1) $ 2,413 6.5 % $ 4,212 13.4 % Business-to-business and other receivables (2) 34,628 93.5 % 27,232 86.6 % Total net accounts receivable $ 37,041 100.0 % $ 31,444 100.0 % (1) Rental includes Medicare, Medicaid/other government, private insurance and patient pay. ( 2 ) Business-to business receivables included one customer with a gross accounts receivable balance of $16,198 and $10,394 as of December 31, 2018 and December 31, 2017, respectively. This customer received extended payment terms through a direct financing plan offered. The Company also has a credit insurance policy in place, which allocated up to $18,000 in coverage as of December 31, 2018 and allocated up to $12,000 in coverage as of December 31, 2017 for this customer with a $400 deductible and 10% retention. The following table sets forth the percentage breakdown of the Company’s net accounts receivable (gross accounts receivable net of allowances) by aging category by invoice due date as of December 31, 2018 and December 31, 2017. As of As of (amounts in thousands) December 31, 2018 December 31, 2017 Net accounts receivable by aging category $ % $ % Held and Unbilled $ 80 0.2 % $ 537 1.7 % Aged 0-90 days 36,245 97.9 % 29,237 93.0 % Aged 91-180 days 425 1.1 % 435 1.4 % Aged 181-365 days 234 0.6 % 602 1.9 % Aged over 365 days 57 0.2 % 633 2.0 % Total net accounts receivable $ 37,041 100.0 % $ 31,444 100.0 % The following table sets forth the accounts receivable allowances as of December 31, 2018 and December 31, 2017: As of As of (amounts in thousands) December 31, 2018 December 31, 2017 Allowances - accounts receivable $ % $ % Doubtful accounts $ 693 1.8 % $ 1,415 4.1 % Rental revenue adjustments 438 1.1 % 947 2.7 % Sales returns 890 2.3 % 904 2.6 % Total allowances - accounts receivable $ 2,021 5.2 % $ 3,266 9.4 % Concentration of credit risk Financial instruments that potentially subject the Company to concentration of credit risk consist principally of cash, cash equivalents, marketable securities and accounts receivable. At times, cash account balances may be in excess of the amounts insured by the Federal Deposit Insurance Corporation (FDIC). However, management believes the risk of loss to be minimal. The Company performs periodic evaluations of the relative credit standing of these institutions and has not experienced any losses on its cash and cash equivalents to date. The Company has also entered into hedging relationships with a single counterparty to offset the forecasted Euro-based revenues. The credit risk has been reduced due to a net settlement arrangement whereby the Company is allowed to net settle transactions with a single net amount payable by one party to the other. Concentration of customers and vendors The Company primarily sells its products to traditional home medical equipment providers, distributors, and resellers in the United States and in foreign countries on a credit basis. The Company also sells its products direct-to-consumers on a primarily prepayment basis. One single customer represented more than 10% of the Company’s total revenue for the years ended December 31, 2018, 2017, and 2016. Two customers represented more than 10% of the Company’s net accounts receivable balance with accounts receivable balances of $16,198 and $4,155, respectively, as of December 31, 2018, and $10,394 and $6,459, respectively, as of December 31, 2017. The Company also rents products direct-to-consumers for insurance reimbursement, which resulted in a customer concentration relating to Medicare’s service reimbursement programs in 2016. Medicare’s service reimbursement programs accounted for 72.6% of rental revenue in the year ended December 31, 2016 and based on total revenue was 12.4% for the year ended December 31, 2016. Medicare did not represent more than 10% of the Company’s total revenue in the years ended December 31, 2018 and 2017. Medicare did not represent more than 10% of the Company’s net accounts receivable balance as of December 31, 2018 and 2017. The Company currently purchases raw materials from a limited number of vendors, which resulted in a concentration of three major vendors. The three major vendors supply the Company with raw materials used to manufacture the Company’s products. For the year ended December 31, 2018, the Company’s three major vendors accounted for 20.0%, 11.9% and 10.2%, respectively, of total raw material purchases. For the year ended December 31, 2017, the Company’s three major vendors accounted for 19.7%, 15.4% and 9.5%, respectively, of total raw material purchases. A portion of revenue is earned from sales outside the United States. Approximately 74.8% of the non-U.S. revenue for the year ended December 31, 2018 was invoiced in Euros. A breakdown of the Company’s revenue from U.S. and non-U.S. sources for the years ended December 31, 2018, 2017 and 2016 is as follows: Years ended December 31, (amounts in thousands) 2018 2017 2016 U.S. revenue $ 280,778 $ 193,919 $ 152,723 Non-U.S. revenue 77,333 55,519 50,106 Total revenue $ 358,111 $ 249,438 $ 202,829 Inventories Inventories are stated at the lower of cost or market and net realizable value. Cost is determined using a standard cost method, including material, labor and manufacturing overhead, whereby the standard costs are updated at least quarterly to reflect approximate actual costs using the first-in, first-out (FIFO) method. The Company records adjustments at least quarterly to inventory for potentially excess, obsolete, slow-moving or impaired items. The Company recorded noncurrent inventory related to inventories that are expected to be realized or consumed after one year of $1,085 and $644 as of December 31, 2018 and 2017, respectively. Noncurrent inventories are primarily related to raw materials purchased in bulk to support long-term expected repairs to reduce costs and are classified in other assets. December 31, (amounts in thousands) 2018 2017 Raw materials and work-in-progress $ 24,980 $ 16,324 Finished goods 2,756 2,917 Less: reserves (665 ) (399 ) Inventories $ 27,071 $ 18,842 Property and equipment Property and equipment are stated at cost. Depreciation and amortization are calculated using the straight-line method over the assets’ estimated useful lives as follows: Rental equipment 1.5-5 years Manufacturing equipment and tooling 3-5 years Computer equipment and software 2-3 years Furniture and equipment 3-5 years Leasehold improvements Lesser of estimated useful life or remai

Goodwill and Other Identifiable

Goodwill and Other Identifiable Intangible Assets	12 Months Ended
	Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill and Other Identifiable Intangible Assets	3. Goodwill and other identifiable intangible assets Goodwill The changes in the carrying amount of goodwill for the years ended December 31, 2018 and 2017 were as follows: (amounts in thousands) Balance as of December 31, 2016 $ — Acquisition 2,154 Translation adjustment 209 Balance as of December 31, 2017 $ 2,363 Translation adjustment (106 ) Balance as of December 31, 2018 $ 2,257 Intangible assets There were no impairments recorded related to the Company’s intangible assets as of December 31, 2018 and 2017. Amortization expense for intangible assets for the years ended December 31, 2018, 2017 and 2016 was $1,265, $507 and $101, respectively. The following tables represent the changes in net carrying values of the intangibles as of the respective dates: Average estimated Gross (amounts in thousands) useful lives carrying Accumulated December 31, 2018 (in years) amount amortization Net amount Licenses 10 $ 185 $ 155 $ 30 Patents and websites 5 4,164 1,640 2,524 Customer relationships 4 1,373 572 801 Non-compete agreement 2.3 229 154 75 Commercials 2-3 633 308 325 Total $ 6,584 $ 2,829 $ 3,755 Average estimated Gross (amounts in thousands) useful lives carrying Accumulated December 31, 2017 (in years) amount amortization Net amount Licenses 10 $ 185 $ 137 $ 48 Patents and websites 5 4,173 959 3,214 Customer relationships 4 1,437 240 1,197 Non-compete agreement 3 240 52 188 Commercials 2-3 303 233 70 Total $ 6,338 $ 1,621 $ 4,717 Annual estimated amortization expense for each of the succeeding fiscal years is as follows: (amounts in thousands) Intangible Years ending December 31, amortization 2019 $ 1,234 2020 1,132 2021 844 2022 545 2023 — Thereafter — Total $ 3,755

Current Liabilities

Current Liabilities	12 Months Ended
	Dec. 31, 2018
Payables And Accruals [Abstract]
Current Liabilities	4. Current liabilities Accounts payable and accrued expenses as of December 31, 2018 and 2017 consisted of the following: December 31, (amounts in thousands) 2018 2017 Accounts payable $ 13,720 $ 9,541 Accrued inventory (in-transit and unvouchered receipts) and trade payables 9,597 7,252 Accrued purchasing card liability 2,089 2,381 Accrued franchise, sales and use taxes 518 479 Other accrued expenses 862 973 Accounts payable and accrued expenses $ 26,786 $ 20,626 Accrued payroll as of December 31, 2018 and 2017 consisted of the following: December 31, (amounts in thousands) 2018 2017 Accrued bonuses $ 4,780 $ 3,086 Accrued wages and other payroll related items 3,494 1,746 Accrued vacation 1,959 1,338 Accrued employee stock purchase plan deductions 1,174 707 Accrued payroll $ 11,407 $ 6,877

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	5. Income taxes The components of the Company’s income before provision for income taxes are as follows: Years ended December 31, (amounts in thousands) 2018 2017 2016 United States $ 40,245 $ 29,121 $ 22,725 Foreign 210 535 — Income before provision for income taxes $ 40,455 $ 29,656 $ 22,725 The provision for income taxes consists of the following: Years ended December 31, (amounts in thousands) 2018 2017 2016 Current tax expense (benefit) Federal $ — $ 245 $ 451 State (40 ) 240 776 Foreign 171 206 — Total current tax expense 131 691 1,227 Deferred tax expense (benefit) Federal (9,774 ) 8,709 1,357 State (1,630 ) 92 590 Foreign (117 ) (71 ) — Total deferred tax expense (benefit) (11,521 ) 8,730 1,947 Tax benefit for change in valuation allowance — (767 ) (968 ) Total deferred tax expense (benefit), net (11,521 ) 7,963 979 Income tax expense (benefit) $ (11,390 ) $ 8,654 $ 2,206 The components of deferred tax assets and liabilities consist of the following: As of December 31, (amounts in thousands) 2018 2017 Deferred tax assets (liabilities) Accrued expenses $ 8,033 $ 5,669 Net operating loss and credit carryforward 19,805 10,378 Allowance, reserves and other 3,490 3,301 Stock-based compensation 3,253 2,598 Deferred tax assets 34,581 21,946 Property, plant, and equipment (4,683 ) (3,658 ) Total $ 29,898 $ 18,288 Reconciliation of the federal statutory income tax rate to the effective income tax rate for the last three years is as follows: Years ended December 31, 2018 2017 2016 U.S. Statutory rate 21.00 % 34.00 % 34.00 % State income taxes, net of federal benefit (3.73 ) 0.37 0.88 Stock-based compensation (45.01 ) (30.40 ) (23.74 ) Change in valuation allowance — (2.59 ) (4.26 ) R&D credit, net of reserve (1.39 ) (1.43 ) (1.75 ) Expiration of net operating losses — 2.76 4.51 Effect of U.S tax law change — 25.55 — Other 0.98 0.92 0.07 Effective income tax rate (28.15)% 29.18 % 9.71 % On December 22, 2017, TCJA was enacted into law, which significantly changes existing U.S. tax law and includes numerous provisions that affect the Company’s business. Changes include, but are not limited to, a corporate tax rate decrease from 34% to 21% effective for tax years beginning after December 31, 2017, expensing of capital expenditures, the transition of U.S. international taxation from a worldwide tax system to a territorial system, a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings, and limitations on the deductibility of certain executive compensation and other deductions As of December 31, 2018, the Company completed its evaluation and analysis of the TCJA and there was no additional adjustment to the provisional amount recorded in the fourth quarter of 2017. The Company operates in several taxing jurisdictions, including U.S. federal, multiple U.S. states and the Netherlands. The statute of limitations has expired for all tax years prior to 2015 for federal and 2014 to 2015 for various state tax purposes. However, the net operating loss generated on the Company’s federal and state tax returns in prior years may be subject to adjustments by the federal and state tax authorities. As of December 31, 2018, the Company had $67,088 and $27,661 of federal and state net operating loss carryforwards, respectively, that begin to expire in 2026 and 2028 for federal and state purposes, respectively, if not utilized. As of December 31, 2018, the Company had federal and California research and development credit carryforward of $2,743 and $2,800, respectively. The federal credit will begin to expire in 2022; the California credit has indefinite carryforward. Utilization of the Company’s net operating loss and tax credit carryforwards may be subject to annual limitations arising from ownership change limitations provided by the Internal Revenue Code and similar state provisions. Such annual limitations could result in the expiration of the net operating loss and tax credit carryforwards before their utilization. The Company assess the available positive and negative evidence to estimate whether sufficient future taxable income will be generated to permit the use of deferred tax assets. As of December 31, 2018, the Company determined that it is more likely than not that deferred tax assets are realizable due the increase in income before income tax expense (benefit). Accordingly, the Company did not record a valuation allowance as of December 31, 2018. As of December 31, 2017, the Company released $767 of valuation allowance that had been established against deferred tax assets for California net operating losses that expired in 2017. As a result, the Company did not record a valuation allowance as of December 31, 2017. The Company recognizes interest accrued and penalties related to unrecognized tax benefits as income tax expense. No interest or penalties were recognized during the periods presented. Included in the balance of unrecognized tax benefits as of December 31, 2018, 2017 and 2016, were $1,294, $1,062 and $934, respectively, of tax benefits that, if recognized, would affect the effective tax rate. The Company believes that there will be no significant increases or decreases to unrecognized tax benefits within the next 12 months. A reconciliation of the beginning and ending amount of unrecognized tax benefit is as follows: December 31, (amounts in thousands) 2018 2017 2016 Reconciliation of liability for unrecognized tax benefits Balance at beginning of period $ 1,062 $ 934 $ 773 Additions based on tax positions related to current year 232 128 161 Balance at end of period $ 1,294 $ 1,062 $ 934

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Stockholders' Equity	6. Stockholders’ equity Common stock Each share of common stock is entitled to one vote. The holders of common stock are also entitled to receive dividends whenever funds are legally available and when declared by the board of directors, subject to the prior rights of holders of other classes of stock outstanding. Preferred stock Pursuant to the amended and restated certificate of incorporation filed by the Company in connection with the completion of its initial public offering, the Company’s board of directors is authorized to issue up to 10,000,000 shares of preferred stock in one or more series and to fix the rights, preferences, privileges and restrictions thereof. These rights, preferences and privileges could include dividend rights, conversion rights, voting rights, redemption rights, liquidation preferences, sinking fund terms and the number of shares constituting any series or the designation of such series, any or all of which may be greater than the rights of common stock. The issuance of preferred stock could adversely affect the voting power of holders of common stock and the likelihood that such holders will receive dividend payments and payments upon liquidation. In addition, the issuance of preferred stock could have the effect of delaying, deferring or preventing change in the Company’s control or other corporate action. As of December 31, 2018 and 2017, no shares of preferred stock were issued or outstanding, and the board of directors has not authorized or designated any rights, preferences, privileges and restrictions for any class of preferred stock. Dividends There were no dividends declared during the years ended December 31, 2018, 2017 and 2016. Stock incentive plans The Company has a 2002 Stock Incentive Plan (2002 Plan) as amended, under which the Company granted options to purchase shares of its common stock. As of December 31, 2018, options to purchase 4,123 shares of common stock remained outstanding under the 2002 Plan. The 2002 Plan was terminated in March 2012 in connection with the adoption of the 2012 Plan, and, accordingly, no new options are available for issuance under this plan. The 2002 Plan continues to govern outstanding awards granted thereunder. The Company has a 2012 Equity Incentive Plan (2012 Plan) under which the Company granted options to purchase shares of its common stock. As of December 31, 2018, options to purchase 168,016 shares of common stock remained outstanding under the 2012 Plan. The 2012 Plan was terminated in connection with the Company’s initial public offering in February 2014, and accordingly, no new options are available for issuance under this plan. The 2012 Plan continues to govern outstanding awards granted thereunder. The Company has a 2014 Equity Incentive Plan (2014 Plan) that provides for the grant of incentive stock options, within the meaning of Section 422 of the Internal Revenue Code, to the Company’s employees and any parent and subsidiary corporation’s employees, and for the grant of nonstatutory stock options, restricted stock, restricted stock units, restricted stock awards, stock appreciation rights, performance units and performance shares to its employees, directors and consultants and its parent and subsidiary corporations’ employees and consultants. As of December 31, 2018, awards with respect to 1,095,964 shares of the Company’s common stock were outstanding, and 1,910,864 shares of common stock remained available for issuance under the 2014 Plan. The shares available for issuance under the 2014 Plan will be increased by any shares returned to the 2002 Plan, 2012 Plan and the 2014 Plan as a result of expiration or termination of awards (provided that the maximum number of shares that may be added to the 2014 Plan pursuant to such previously granted awards under the 2002 Plan and 2012 Plan is 2,328,569 shares). The number of shares available for issuance under the 2014 Plan also is increased annually on the first day of each fiscal year by an amount equal to the least of: • 895,346 shares; • 4% of the outstanding shares of common stock as of the last day of the Company’s immediately preceding fiscal year; or • such other amount as the Company’s board of directors may determine. For the year ended December 31, 2018, an additional 839,054 shares were added to the 2014 Plan share reserve pursuant to the provision described above. Stock options Options typically expire between seven and ten years from the date of grant and vest over one to four year terms. Options have been granted to employees, directors and consultants of the Company, as determined by the board of directors, at the deemed fair market value of the shares underlying the options at the date of grant. The activity for stock options under the Company’s stock plans is as follows: Remaining weighted- Weighted- average Per share average contractual average Price per exercise terms intrinsic Options share price (in years) value Outstanding as of December 31, 2015 2,295,370 $0.60-$46.66 $ 19.36 5.98 $ 21.07 Granted 683,998 44.19-58.95 44.70 Exercised (570,079 ) 0.60-46.66 12.32 Forfeited (53,247 ) 1.17-44.19 28.09 Expired (515 ) 8.70 8.70 Outstanding as of December 31, 2016 2,355,527 0.60-58.95 28.22 5.42 38.95 Vested and exercisable as of December 31, 2016 1,023,865 0.60-46.66 16.61 4.96 50.56 Vested and expected to vest as of December 31, 2016 2,259,811 0.60-46.66 27.95 5.40 39.22 Outstanding as of December 31, 2016 2,355,527 0.60-58.95 28.22 5.42 38.95 Granted 64,498 83.30 83.30 Exercised (520,393 ) 0.60-58.95 24.16 Forfeited (63,173 ) 24.52-58.95 43.74 Expired (33 ) 8.70 8.70 Outstanding as of December 31, 2017 1,836,426 0.60-83.30 30.77 4.58 88.31 Vested and exercisable as of December 31, 2017 1,176,504 0.60-83.30 24.33 4.39 94.75 Vested and expected to vest as of December 31, 2017 1,792,871 0.60-83.30 30.50 4.58 88.58 Outstanding as of December 31, 2017 1,836,426 0.60-83.30 30.77 4.58 88.31 Granted — — — Exercised (708,319 ) 0.60-58.95 24.22 Forfeited (771 ) 24.52-44.19 28.24 Expired — — — Outstanding as of December 31, 2018 1,127,336 0.75-83.30 34.89 3.84 89.28 Vested and exercisable as of December 31, 2018 851,039 0.75-83.30 32.12 3.75 92.05 Vested and expected to vest as of December 31, 2018 1,109,280 $0.75-$83.30 $ 34.75 3.84 $ 89.42 The total intrinsic value of options exercised during the years ended December 31, 2018, 2017, and 2016 was $98,743, $33,931, and $22,228, respectively. The unrecognized compensation expense related to non-vested stock-based compensation granted under the Plans as of December 31, 2018 was $4,072. Stock incentive awards The Company grants restricted stock units (RSUs) and restricted stock awards (RSAs) under the 2014 Plan (Stock Awards). The Stock Awards vest either based solely on the satisfaction of time-based service conditions or on the satisfaction of time-based service conditions combined with performance criteria. Stock Awards are subject to forfeiture if the holder’s services to the Company terminate before vesting. Stock Awards granted with only time-based service vesting conditions generally vest over a four-year service period, as defined in the terms of each award. Stock Awards that vest based on the satisfaction of time-based service conditions combined with performance criteria generally vest over a three-year service and performance period, based on performance criteria established at the time of the award. The portion of the Stock Award that is earned may equal or be less than the targeted number of shares subject to the Stock Award depending on whether the performance criteria are met. Stock Awards activity for the years ended December 31, 2018 and December 31, 2017 are summarized below: Weighted- average grant Performance date fair and value Time-based time-based Total per share Unvested restricted stock units as of December 31, 2016 — — — $ — Granted 42,028 13,109 55,137 90.05 Vested — — — — Forfeited/canceled — — — — Unvested restricted stock units as of December 31, 2017 (1) 42,028 13,109 55,137 $ 90.05 Unvested and expected to vest restricted stock units outstanding as of December 31, 2017 48,589 $ 89.95 Unvested restricted stock units as of December 31, 2017 42,028 13,109 55,137 $ 90.05 Granted 31,877 — 31,877 143.50 Vested (13,742 ) (4,370 ) (18,112 ) 89.35 Forfeited/canceled (1,574 ) — (1,574 ) 106.55 Unvested restricted stock units as of December 31, 2018 (1) 58,589 8,739 67,328 $ 115.16 Unvested and expected to vest restricted stock units outstanding as of December 31, 2018 62,504 $ 115.98 Unvested restricted stock awards outstanding as of December 31, 2016 — — — $ — Granted 20,789 20,785 41,574 91.52 Vested — — — — Forfeited/canceled — — — — Unvested restricted stock awards outstanding as of December 31, 2017 (1) 20,789 20,785 41,574 $ 91.52 Unvested and expected to vest restricted stock awards outstanding as of December 31, 2017 34,051 $ 91.52 Unvested restricted stock awards outstanding as of December 31, 2017 20,789 20,785 41,574 $ 91.52 Granted 22,645 33,964 56,609 130.89 Vested (6,497 ) (6,928 ) (13,425 ) 91.52 Forfeited/canceled — — — — Unvested restricted stock awards outstanding as of December 31, 2018 (1) 36,937 47,821 84,758 $ 115.80 Unvested and expected to vest restricted stock awards outstanding as of December 31, 2018 65,773 $ 115.85 (1 ) Outstanding restricted stock units and restricted stock awards are based on the maximum payout of the targeted number of shares. As of December 31, 2018, the unrecognized compensation cost related to unvested employee restricted stock units and restricted stock awards was $10,091, excluding estimated forfeitures. This amount is expected to be recognized over a weighted-average period of 2.7 years. Employee stock purchase plan The Company’s 2014 Employee Stock Purchase Plan (ESPP) provides for the grant to all eligible employees an option to purchase stock under the ESPP, within the meaning Section 423 of the Internal Revenue Code. The ESPP permits participants to purchase common stock through payroll deductions of up to 15% of their eligible compensation, which includes a participant’s base straight time gross earnings, incentive compensation, bonuses, overtime and shift premium, but exclusive of payments for equity compensation and other similar compensation. A participant may purchase a maximum of 1,500 shares during a purchase period. Amounts deducted and accumulated by the participant are used to purchase shares of the Company’s common stock at the end of each six-month period. The purchase price of the shares will be 85% of the lower of the fair market value of the Company’s common stock on the first trading day of each offering period or on the exercise date. The offering periods are currently approximately six months in length beginning on the first business day on or after March 1 and September 1 of each year and ending on the first business day on or after September 1 and March 1 approximately six months later. As of December 31, 2018, a total of 746,448 shares of common stock were available for sale pursuant to the ESPP. The number of shares available for sale under the ESPP is increased annually on the first day of each fiscal year equal to the least of: • 179,069 shares; • 1.5% of the outstanding shares of the Company’s common stock on the last day of the Company’s immediately preceding fiscal year; or • such other amount as may be determined by the administrator. For the year ended December 31, 2018, an additional 179,069 shares were added to the ESPP share reserve pursuant to the provision described above. Stock-based compensation Stock-based compensation expense recognized for the years ended December 31, 2018, 2017 and 2016 was as follows: Years ended December 31, (amounts in thousands) 2018 2017 2016 Stock-based compensation expense by type of award: Stock option plan awards $ 6,015 $ 7,652 $ 6,850 Restricted stock units and restricted stock awards 5,890 1,447 — Employee stock purchase plan 885 541 444 Total stock-based compensation expense $ 12,790 $ 9,640 $ 7,294 Employee stock-based compensation expense was calculated based on awards of stock options, restricted stock units and restricted stock awards ultimately expected to vest based on the Company’s historical award cancellations. The employee stock-based compensation expense recognized for the years ended December 31, 2018, 2017 and 2016 has been reduced for estimated forfeitures of stock option plan awards at a rate of 7.3%, 7.3% and 6.9%, respectively. The employee stock-based compensation expense recognized for the years ended December 31, 2018 and 2017 was reduced for estimated forfeitures of restricted stock at a rate of 4.7% and 6.0%, respectively. There were no grants of restricted stock units and restricted stock awards for the year ended December 31, 2016. ASC 718 requires forfeitures to be estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. For the years ended December 31, 2018, 2017 and 2016, stock-based compensation expense recognized under ASC 718, included in cost of revenues, sales and marketing expense, general and administrative expense, and research and development expense was as follows: Years ended December 31, (amounts in thousands) 2018 2017 2016 Cost of revenue $ 1,060 $ 845 $ 639 Research and development 1,314 1,015 776 Sales and marketing 2,355 1,558 1,142 General and administrative 8,061 6,222 4,737 Total stock-based compensation expense $ 12,790 $ 9,640 $ 7,294 Valuation assumptions The employee stock-based compensation expense is recognized under ASC 718. Stock-based compensation cost for stock awards is based on the number of shares ultimately expected to vest, estimated at each reporting date based on management’s expectations regarding the relevant performance criteria. The value of the award that is ultimately expected to vest is recognized as expense on a straight-line basis over the employee’s requisite service period for stock awards with a time-based service condition and on a graded vesting basis over the employee’s requisite service period for stock awards with performance and time-based service conditions. Stock-based compensation cost for stock options and employee stock purchase plan are determined at the grant date using the Black-Scholes option pricing model. The following table displays the assumptions that have been applied to estimate the fair value of stock option awards on the date of grant using the Black-Scholes option pricing model. During 2018, the Company did not grant any stock option awards. 2017 2016 Expected term (years) 3.54-4.00 3.54-5.48 Risk free interest rate 1.65-1.73% 1.00-1.40% Expected dividend yield None None Volatility 41.61-42.15% 43.95-45.93% Under these assumptions, the total weighted-average fair value of stock options granted during the years ended December 31, 2017 and 2016 was $8,929 and $6,408, respectively. The Company made no stock option grants during the year ended December 31, 2018. The following table displays the assumptions that have been applied to estimate the fair value of the Company’s shares to be issued under the ESPP using the Black-Scholes option pricing model. 2018 2017 2016 Expected term (years) 0.50 0.50 0.50 Risk free interest rate 1.63-2.46% 1.15-1.63% 1.15-1.32% Expected dividend yield None None None Volatility 37.34-44.00% 42.35-45.34% 43.28-44.81% 401(k) retirement savings plan The Company maintains a 401(k) retirement savings plan for the benefit of eligible employees. Under the terms of this plan, eligible employees are able to make contributions to the plan on a tax-deferred basis. The Company began matching employees’ contributions, effective January 1, 2017. The Company contributed $865, net of forfeitures, and $557, net of forfeitures to the 401(k) plan for the years ended December 31, 2018 and 2017, respectively. The Company made no contributions to the 401(k) plan for the years ended December 31, 2016.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and contingencies Leases and non-cancelable contractual obligations The Company leases its facilities and certain equipment under operating leases that expire through September 2024. At December 31, 2018, the minimum aggregate payments due under operating leases and specified non-cancelable contractual obligations, which consist of software license and maintenance agreements, Non-cancelable Operating Related party contractual (amounts in thousands) leases leases obligations Total 2019 $ 2,450 $ 31 $ 578 $ 3,059 2020 2,212 10 578 2,800 2021 1,593 — 457 2,050 2022 1,273 — — 1,273 2023 1,215 — — 1,215 Thereafter 917 — — 917 Total $ 9,660 $ 41 $ 1,613 $ 11,314 As a result of the MedSupport acquisition, the Company leases a property owned by a related party. Rent expense for the property was $33 and $21 for the years ended December 31, 2018 and 2017, respectively. Rent expense of $1,638, $1,148 and $1,028 for the years ended December 31, 2018, 2017 and 2016, respectively, was included in the accompanying consolidated statements of comprehensive income. Purchase obligations The Company had approximately $61,000 of outstanding purchase orders with its outside vendors and suppliers as of December 31, 2018. Warranty obligation The following table identifies the changes in the Company’s aggregate product warranty liabilities for the years ended December 31, 2018, 2017 and 2016: December 31, (amounts in thousands) 2018 2017 2016 Product warranty liability at beginning of period $ 6,171 $ 3,480 $ 1,973 Accruals for warranties issued 7,693 5,275 3,123 Adjustments related to preexisting warranties (including changes in estimates) 90 200 118 Settlements made (in cash or in kind) (4,424 ) (2,784 ) (1,734 ) Product warranty liability at end of period $ 9,530 $ 6,171 $ 3,480 Legislation and HIPAA The healthcare industry is subject to numerous laws and regulations of federal, state and local governments. These laws and regulations include, but are not necessarily limited to, matters such as licensure, accreditation, government healthcare program participation requirements, reimbursement for patient services, and Medicare and Medicaid fraud and abuse. Government activity has continued with respect to investigations and allegations concerning possible violations of fraud and abuse statutes and regulations by healthcare providers. Violations of these laws and regulations could result in exclusion from government healthcare programs together with the imposition of significant fines and penalties, as well as significant repayments for patient services previously billed. The Company believes that it is in compliance in all material respects with applicable fraud and abuse regulations and other applicable government laws and regulations. Compliance with such laws and regulations can be subject to future government review and interpretation as well as regulatory actions unknown or unasserted at this time. The Health Insurance Portability and Accountability Act of 1996 (HIPAA) ensures health insurance portability, reduces healthcare fraud and abuse, guarantees security and privacy of health information, and enforces standards for health information. The Health Information Technology for Economic and Clinical Health Act (HITECH Act) imposes notification requirements of certain security breaches relating to protected health information. The Company believes that it complies in all material respects with the provisions of those regulations that are applicable to the Company’s business. Legal proceedings The Company is party to various legal proceedings arising in the normal course of business. The Company carries insurance, subject to specified deductibles under the policies, to protect against losses from certain types of legal claims. At this time, the Company does not anticipate that any of these other proceedings will have a material adverse effect on the Company’s business. Regardless of the outcome, litigation can have an adverse impact on the Company because of defense and settlement costs, diversion of management resources, and other factors.

Foreign Currency Exchange Contr

Foreign Currency Exchange Contracts and Hedging	12 Months Ended
	Dec. 31, 2018
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Foreign currency exchange contracts and hedging	8. Foreign currency exchange contracts and hedging As of December 31, 2018 and December 31, 2017, the Company’s total non-designated and designated derivative contracts had notional amounts totaling approximately $2,336 and $21,374, respectively, and $2,350 and $13,818, respectively. These contracts were comprised of offsetting contracts with the same counterparty, each expires within one to twelve months. During the years ended December 31, 2018, 2017, and 2016, these contracts had, net of tax, an unrealized gain of $404, an unrealized loss of $121, and an unrealized gain of $47, respectively. The nonperformance risk of the Company and the counterparty did not have a material impact on the fair value of the derivatives. During the years ended December 31, 2018, 2017 and 2016, there were no ineffective portions relating to these hedges and the hedges remained effective through their respective settlement dates. As of December 31, 2018, the Company had twenty-nine designated hedges and four non-designated hedges. As of December 31, 2017, the Company had eighteen designated hedges and three non-designated hedges.

Quarterly Summary of Informatio

Quarterly Summary of Information (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly summary of information (unaudited)	9. Quarterly summary of information (unaudited) The following table sets forth the Company’s unaudited quarterly statements of income data in dollars for each of the eight quarters in the period ended December 31, 2018. The Company has prepared the quarterly statements of income data on a basis consistent with the audited financial statements. In the opinion of management, the financial information reflects all adjustments, consisting only of normal recurring adjustments, which the Company considers necessary for a fair presentation of this data. The results of historical periods are not necessarily indicative of the results of operations for any future period. (amounts in thousands, except share and per share amounts) Quarterly Results 2018 Q1 March Q2 June Q3 September Q4 December Total revenue $ 79,051 $ 97,238 $ 95,291 $ 86,531 Gross profit 37,727 48,470 48,813 43,570 Income before benefit for income taxes 9,687 13,646 11,299 5,823 Benefit for income taxes (1,071 ) (964 ) (5,133 ) (4,222 ) Net income 10,758 14,610 16,432 10,045 Net income per share attributable to common stockholders: Basic $ 0.51 $ 0.69 $ 0.77 $ 0.47 Diluted $ 0.48 $ 0.65 $ 0.73 $ 0.44 Weighted-average number of shares used in calculating net income per share attributable to common stockholders: Basic common shares 21,026,154 21,172,170 21,324,256 21,544,202 Diluted common shares 22,295,213 22,503,749 22,659,052 22,600,038 (amounts in thousands, except share and per share amounts) Quarterly Results 2017 Q1 March Q2 June Q3 September Q4 December Total revenue $ 52,500 $ 64,121 $ 69,030 $ 63,787 Gross profit 25,744 31,567 33,170 30,756 Income before provision (benefit) for income taxes 5,879 9,166 8,817 5,794 Provision (benefit) for income taxes (53 ) 828 1,479 6,400 Net income (loss) 5,932 8,338 7,338 (606 ) Net income (loss) per share attributable to common stockholders: Basic $ 0.29 $ 0.40 $ 0.35 $ (0.03 ) Diluted $ 0.27 $ 0.38 $ 0.33 $ (0.03 ) Weighted-average number of shares used in calculating net income (loss) per share attributable to common stockholders: Basic common shares 20,489,532 20,622,320 20,753,789 20,869,589 Diluted common shares 21,579,721 21,848,359 21,998,660 22,167,358 Earnings per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly amounts will not necessarily equal the total for the year.

Schedule II_ Valuation and Qual

Schedule II: Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2018
Valuation And Qualifying Accounts [Abstract]
Schedule II: Valuation and Qualifying Accounts	Balance at Beginning Balance at (amounts in thousands) of Year Additions Deletions Adjustments End of Year Year ended December 31, 2018 Allowance for doubtful accounts (1) $ 1,415 $ 1,685 $ 2,677 $ 270 $ 693 Allowance for sales returns (2) 904 15,834 15,848 — 890 Allowance for rental revenue adjustments (3) 947 2,678 2,917 (270 ) 438 Allowance for rental asset loss (4) 754 408 568 — 594 Year ended December 31, 2017 Allowance for doubtful accounts (1) $ 1,869 $ 3,864 $ 4,418 $ 100 $ 1,415 Allowance for sales returns (2) 585 9,909 9,590 — 904 Allowance for rental revenue adjustments (3) 6,078 5,057 10,088 (100 ) 947 Allowance for rental asset loss (4) 725 561 532 — 754 Year ended December 31, 2016 Allowance for doubtful accounts (1) $ 1,664 $ 3,580 $ 2,575 $ (800 ) $ 1,869 Allowance for sales returns (2) 366 7,502 7,283 — 585 Allowance for rental revenue adjustments (3) 4,115 10,777 9,614 800 6,078 Allowance for rental asset loss (4) 850 455 580 — 725 (1) The additions to the allowance for doubtful accounts represent the estimates of bad debt expense based upon factors for which the company evaluates the collectability of accounts receivable, with actual recoveries netted into additions. Deductions are the actual write-offs of the receivables. (2) The additions to the allowance for sales returns represent estimates of returns based upon historical returns experience, primarily for the direct-to-consumer sales channel. Deductions are the actual returns of products. (3) The additions to the allowance for rental revenue adjustments represent estimates of revenue adjustments that will need to be recorded for billing adjustments on rental revenue, net of recoveries. Deductions are the actual adjustments and write-offs of the rental receivables for such revenue adjustments. ( 4 ) The allowance for rental asset loss is based on estimated losses of the Company’s rental assets that will potentially be lost, stolen or unrecoverable from the patient. Deductions are the actual write-offs of the rental assets.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of presentation The consolidated financial statements of the Company have been prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP).
Basis of Consolidation	Basis of consolidation The consolidated financial statements include the accounts of Inogen, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated.
Accounting Estimates	Accounting estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Management bases these estimates and assumptions upon historical experience, existing and known circumstances, authoritative accounting pronouncements and other factors that management believes to be reasonable. Significant areas requiring the use of management estimates relate to revenue recognition and determining the stand-alone selling price (SSP) of performance obligations, inventory and rental asset valuations and write-downs, accounts receivable allowances for bad debts, returns and adjustments, warranty expense, stock compensation expense, depreciation and amortization, income tax provision and uncertain tax positions, fair value of financial instruments, and fair value of acquired intangible assets and goodwill. Actual results could differ from these estimates.
Revenue	Revenue The Company generates revenue primarily from sales and rentals of its products. The Company’s products consist of its proprietary line of oxygen concentrators and related accessories. Other revenue, which is included in sales revenue on the Statements of Comprehensive Income, primarily comes from service contracts, replacement parts and freight revenue for product shipments. Sales revenue Revenue is recognized upon transfer of control of promised products or services to customers in an amount that reflects the consideration the Company expects to receive in exchange for those products or services. Revenue from product sales is generally recognized upon shipment of the product but is deferred for certain transactions when control has not yet transferred to the customer. The Company’s product is generally sold with a right of return and the Company may provide other incentives, which are accounted for as variable consideration when estimating the amount of revenue to recognize. Returns and incentives are estimated at the time sales revenue is recognized. The provisions for estimated returns are made based on known claims and estimates of additional returns based on historical data and future expectations. Sales revenue incentives within the Company’s contracts are estimated based on the most likely amounts expected on the related sales transaction and recorded as a reduction to revenue at the time of sale in accordance with the terms of the contract. The Company also offers a lifetime warranty for direct-to-consumer sales of its portable oxygen concentrators. For a fixed price, the Company agrees to provide a fully functional portable oxygen concentrator for the remaining life of the patient. Lifetime warranties are only offered to patients upon the initial sale of portable oxygen concentrators directly from the Company and are non-transferable. Lifetime warranties are considered to be a distinct performance obligation that are accounted for separately from its sale of portable oxygen concentrators with a standard warranty of three years . The revenue is allocated to the distinct lifetime warranty performance obligation based on a relative SSP method. The Company has vendor-specific objective evidence of the selling price for its equipment. To determine the selling price of the lifetime warranty, the Company uses its best estimate of the SSP for the distinct performance obligation as the lifetime warranty is neither separately priced nor is the selling price available through third-party evidence. To calculate the selling price associated with the lifetime warranties, management considers the profit margins of service revenue, the average estimated cost of lifetime warranties and the price of extended warranties. Revenue from the distinct lifetime warranty is deferred after the delivery of the equipment and recognized based on an estimated mortality rate over five years, which is the estimated performance period of the contract based on the average patient life expectancy. Revenue from the sale of the Company’s repair services is recognized when the performance obligations are satisfied and collection of the receivables is probable. Other revenue from the sale of replacement parts is generally recognized when product is shipped to customers. Freight revenue consists of fees associated with the deployment of products internationally and domestically when expedited freight options are requested or when minimum order quantities are not met. Freight revenue is generally recognized upon shipment of the product but is deferred if control has not yet transferred to the customer. Shipping and handling costs for sold products and rental assets shipped to the Company’s customers are included on the consolidated statement of comprehensive income as part of cost of sales revenue and cost of rental revenue, respectively. The payment terms and conditions of customer contracts vary by customer type and the products and services offered. For certain products or services and customer types, the Company requires payment before the products or services are delivered to the customer. The timing of sales revenue recognition, billing and cash collection results in billed accounts receivable and deferred revenue in the consolidated balance sheet. Contract liabilities primarily consist of deferred revenue related to lifetime warranties on direct-to-consumer sales revenue when cash payments are received in advance of services performed under the contract. The contract with the customer states the final terms of the sale, including the description, quantity, and price of each product or service purchase. The increase in deferred revenue related to lifetime warranties were primarily driven by $6,909 and $4,290 of payments received in advance of satisfying performance obligations for the years ended December 31, 2018 and December 31, 2017, respectively, par and $752 . $14,874 10,820 The Company elected to apply the practical expedient in accordance with Accounting Standards Codification (ASC) — Revenue Recognition did not evaluate contracts of one year or less for the existence of a significant financing component The Company’s sales revenue is primarily derived from the sale of its Inogen One systems, Inogen At Home systems, and related accessories to individual consumers, home medical equipment providers, distributors, the Company’s private label partner and resellers worldwide. Sales revenue is classified into two areas: business-to-business sales and direct-to-consumer sales. The following table sets forth the Company’s sales revenue disaggregated by sales channel and geographic region: (amounts in thousands) Years ended December 31, Revenue by region and category 2018 2017 2016 Business-to-business domestic sales $ 116,581 $ 83,390 $ 56,605 Business-to-business international sales 77,333 55,519 50,106 Direct-to-consumer domestic sales 142,101 86,583 61,459 Total sales revenue $ 336,015 $ 225,492 $ 168,170 Rental revenue The Company recognizes equipment rental revenue over the non-cancelable lease term, which is one month, less estimated adjustments, in accordance with ASC 840— Leases The lease term begins on the date products are shipped to patients and are recorded at amounts estimated to be received under reimbursement arrangements with third-party payors, including Medicare, private payors, and Medicaid. Due to the nature of the industry and the reimbursement environment in which the Company operates, certain estimates are required to record net revenue and accounts receivable at their net realizable values. Inherent in these estimates is the risk that they will have to be revised or updated as additional information becomes available. Specifically, the complexity of many third-party billing arrangements and the uncertainty of reimbursement amounts for certain services from certain payors may result in adjustments to amounts originally recorded. Such adjustments are typically identified and recorded at the point of cash application, claim denial or account review. The Company adjusts revenue for historical trends on revenue adjustments due to timely filings, deaths, hospice, and other types of analyzable adjustments on a monthly basis. Accounts receivable are reduced by an allowance for doubtful accounts which provides for those accounts from which payment is not expected to be received although product was delivered and revenue was earned. The determination that an account is uncollectable and the ultimate write-off of that account occurs once collection is considered to be highly unlikely, and it is written-off and charged to the allowance at that time. Amounts billed but not earned due to the timing of the billing cycle are deferred and recognized in revenue on a straight-line basis over the monthly billing period. For example, if the first day of the billing period does not fall on the first of the month, then a portion of the monthly billing period will fall in the subsequent month and the related revenue and cost would be deferred based on the service days in the following month. Rental revenue is recognized as earned, less estimated adjustments. Revenue not billed at the end of the period is reviewed for the likelihood of collections and accrued. The rental revenue stream is not guaranteed and payment will cease if the patient no longer needs oxygen or returns the equipment. Revenue recognized is at full estimated allowable amounts; transfers to secondary insurances or patient responsibility have no net effect on revenue. Rental revenue is earned for that entire month if the patient is on service on the first day of the 30-day period commencing on the recurring date of service for a particular claim, regardless if there is a change in condition or death after that date. Included in rental revenue are unbilled amounts for which the revenue recognition criteria had been met as of period-end but were not yet billed to the payor. The estimate of net unbilled rental revenue recognized is based on historical trends and estimates of future collectability. In addition, the Company estimates potential future adjustments and write-offs of these unbilled amounts and includes these estimates in the allowance for adjustments and write-offs of rental revenue which is netted against gross receivables.
Fair Value of Financial Instruments	Fair value of financial instruments The Company’s financial instruments consist of cash and cash equivalents, marketable securities, accounts receivable, accounts payable and accrued expenses. The carrying values of its financial instruments approximate fair value based on their short-term nature. Imputed interest associated with the Company’s non-interest bearing debt was insignificant and was appropriately recognized in the respective periods. Fair value accounting ASC 820 — Fair Value Measurements and Disclosures Level input Input definition Level 1 Inputs are unadjusted, quoted prices for identical assets or liabilities in active markets at the measurement date. Level 2 Inputs, other than quoted prices included in Level 1 that are observable for the asset or liability through corroboration with market data at the measurement date. Level 3 Unobservable inputs that reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. The Company obtained the fair value of its available-for-sale securities, which are not in active markets, from a third-party professional pricing service using quoted market prices for identical or comparable instruments, rather than direct observations of quoted prices in active markets. The Company's professional pricing service gathers observable inputs for all of its fixed income securities from a variety of industry data providers (e.g., large custodial institutions) and other third-party sources. Once the observable inputs are gathered, all data points are considered and the fair value is determined. The Company validates the quoted market prices provided by its primary pricing service by comparing their assessment of the fair values against the fair values provided by its investment managers. The Company's investment managers use similar techniques to its professional pricing service to derive pricing as described above. As all significant inputs were observable, derived from observable information in the marketplace or supported by observable levels at which transactions are executed in the marketplace, the Company has classified its marketable securities within Level 2 of the fair value hierarchy. The following table summarizes fair value measurements by level for the assets measured at fair value on a recurring basis for cash, cash equivalents and marketable securities: As of December 31, 2018 Gross Cash Adjusted unrealized and cash Marketable (amounts in thousands) cost gains (losses) Fair value equivalents securities Cash $ 33,671 $ — $ 33,671 $ 33,671 $ — Level 1: Money market accounts 158,438 — 158,438 158,438 — Level 2: Corporate bonds 13,629 (16 ) 13,613 — 13,613 U.S. Treasury securities 34,620 7 34,627 4,525 30,102 Total $ 240,358 $ (9 ) $ 240,349 $ 196,634 $ 43,715 As of December 31, 2017 Gross Cash Adjusted unrealized and cash Marketable (amounts in thousands) cost losses Fair value equivalents securities Cash $ 46,237 $ — $ 46,237 $ 46,237 $ — Level 1: Money market accounts 93,430 — 93,430 93,430 — Level 2: Certificates of deposit 11,010 (4 ) 11,006 490 10,516 Corporate bonds 20,789 (21 ) 20,768 2,796 17,972 Agency mortgage-backed securities 2,005 (1 ) 2,004 — 2,004 U.S. Treasury securities 499 — 499 — 499 Total $ 173,970 $ (26 ) $ 173,944 $ 142,953 $ 30,991 The following table summarizes the estimated fair value of the Company’s investments in marketable securities, classified by the contractual maturity date of the securities: December 31, (amounts in thousands) 2018 Due within one year $ 43,715 Due in one year through five years — Total $ 43,715
Derivative Instruments and Hedging Activities	Derivative instruments and hedging activities The Company transacts business in foreign currencies and has international sales and expenses denominated in foreign currencies, subjecting the Company to foreign currency risk. The Company has entered into foreign currency forward contracts, generally with maturities of twelve months or less, to reduce the volatility of cash flows primarily related to forecasted revenue denominated in certain foreign currencies. These contracts allow the Company to sell Euros in exchange for U.S. dollars at specified contract rates. Forward contracts are used to hedge forecasted sales over specific months. Changes in the fair value of these forward contracts designed as cash flow hedges are recorded as a component of accumulated other comprehensive income (loss) income within stockholders’ equity and are recognized in the consolidated statements of comprehensive income during the period which approximates the time the corresponding sales occur. The Company may also enter into foreign exchange contracts that are not designated as hedging instruments for financial accounting purposes. These contracts are generally entered into to offset the gains and losses on certain asset and liability balances until the expected time of repayment. Accordingly, any gains or losses resulting from changes in the fair value of the non-designated contracts are reported in other expense, net in the consolidated statements of comprehensive income. The gains and losses on these contracts generally offset the gains and losses associated with the underlying foreign currency-denominated balances, which are also reported in other income (expense), net. The Company records the assets or liabilities associated with derivative instruments and hedging activities at fair value based on Level 2 inputs in other current assets or other current liabilities, respectively, in the consolidated balance sheet. The Company had a receivable of $472 and a payable of $66 as of December 31, 2018 and 2017, respectively. The Company classifies the foreign currency derivative instruments within Level 2 in the fair value hierarchy as the valuation inputs are based on quoted prices and market observable data of whether it is designated and qualifies for hedge accounting. The Company documents the hedging relationship and its risk management objective and strategy for undertaking the hedge, the hedging instrument, the hedged transaction, the nature of the risk being hedged, how the hedging instrument’s effectiveness in offsetting the hedged risk will be assessed prospectively and retrospectively, and a description of the method used to measure ineffectiveness. The Company assesses hedge effectiveness and ineffectiveness at a minimum quarterly but may assess it monthly. For derivative instruments that are designed and qualify as part of a cash flow hedging relationship, the effective portion of the gain or loss on the derivative is reported in other comprehensive income (loss) and reclassified into earnings in the same periods during which the hedged transaction affects earnings. Gains and losses on the derivative representing either hedge ineffectiveness or hedge components excluded from the assessment of effectiveness are recognized in current period earnings. The Company will discontinue hedge accounting prospectively when it determines that the derivative is no longer effective in offsetting cash flows attributable to the hedge risk. The cash flow hedge is de-designated because a forecasted transaction is not probable of occurring, or management determines to remove the designation of the cash flow hedge. In all situations in which hedge accounting is discontinued and the derivative remains outstanding, the Company continues to carry the derivative at its fair value on the balance sheet and recognizes any subsequent changes in the fair value in earnings. When it is probable that a forecasted transaction will not occur, the Company will discontinue hedge accounting and recognize immediately in earnings gains and losses that were accumulated in other comprehensive income (loss) related to the hedging relationship.
Accumulated Other Comprehensive Income (Loss)	Accumulated other comprehensive income (loss) The components of accumulated other comprehensive income (loss) were as follows: As of December 31, 2018 Foreign Unrealized Unrealized Accumulated currency gains (losses) on gains (losses) other translation marketable on cash comprehensive (amounts in thousands) adjustments securities flow hedges income Balance as of December 31, 2017 $ 363 $ (17 ) $ (74 ) $ 272 Other comprehensive gain 31 17 404 452 Balance as of December 31, 2018 $ 394 $ — $ 330 $ 724 As of December 31, 2017 Foreign Unrealized Unrealized Accumulated currency gains (losses) on gains (losses) other translation marketable on cash comprehensive (amounts in thousands) adjustments securities flow hedges income (loss) Balance as of December 31, 2016 $ — $ (82 ) $ 47 $ (35 ) Other comprehensive gain (loss) 363 65 (121 ) 307 Balance as of December 31, 2017 $ 363 $ (17 ) $ (74 ) $ 272 Comprehensive income (loss) is the total net earnings and all other non-owner changes in equity. Except for net income and unrealized gains and losses on cash flow hedges, the Company does not have any transactions or other economic events that qualify as comprehensive income (loss).
Cash, Cash Equivalents, and Marketable Securities	Cash, cash equivalents, and marketable securities The Company considers all short-term highly liquid investments with a maturity of three months or less to be cash equivalents. The Company’s marketable debt securities have been classified and accounted for as available-for-sale. Cash equivalents are recorded at cost plus accrued interest, which is considered adjusted cost, and approximates fair value. Marketable debt securities are included in cash equivalents and marketable securities based on the maturity date of the security. Short-term investments are included in marketable securities in the current period presentation. The Company considers investments with maturities greater than three months, but less than one year, to be marketable securities. Investments are reported at fair value with realized and unrealized gains or losses reported in other income (expense), net. The Company reviews its investments to identify and evaluate investments that have an indication of possible impairment. Factors considered in determining whether a loss is temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition and near-term prospects of the investee, and the Company's intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in market value. Credit losses and other-than-temporary impairments are declines in fair value that are not expected to recover and are charged to other income (expense), net. Cash, cash equivalents, and marketable securities consist of the following: (amounts in thousands) December 31, Cash and cash equivalents 2018 2017 Cash $ 33,671 $ 46,237 Money market accounts 158,438 93,430 Certificates of deposit — 490 Corporate bonds — 2,796 U.S. Treasury securities 4,525 — Total cash and cash equivalents $ 196,634 $ 142,953 Marketable securities Certificates of deposit $ — $ 10,516 Corporate bonds 13,613 17,972 Agency mortgage-backed securities — 2,004 U. S. Treasury securities 30,102 499 Total marketable securities $ 43,715 $ 30,991
Accounts Receivable and Allowance for Bad Debts, Returns, and Adjustments	Accounts receivable and allowance for bad debts, returns, and adjustments Accounts receivable are customer obligations due under normal sales and rental terms. The Company performs credit evaluations of the customers’ financial condition and generally does not require collateral. The allowance for doubtful accounts is maintained at a level that, in management’s opinion, is adequate to absorb potential losses related to accounts receivable and is based upon the Company’s continuous evaluation of the collectability of outstanding balances. Management’s evaluation takes into consideration such factors as past bad debt experience, economic conditions and information about specific receivables. The Company’s evaluation also considers the age and composition of the outstanding amounts in determining their net realizable value. The allowance for doubtful accounts is based on estimates, and ultimate losses may vary from current estimates. As adjustments to these estimates become necessary, they are reported in general and administrative expense in the periods in which they become known. This allowance is increased by bad debt provisions charged to bad debt expense, net of recoveries, in operating expense and is reduced by direct write-offs. The Company generally does not allow returns from providers for reasons not covered under its standard warranty. Therefore, provision for returns applies primarily to direct-to-consumer sales. This reserve is calculated based on actual historical return rates under the Company’s 30-day return program and is applied to the related sales revenue for the last month of the quarter reported. The Company also records an allowance for rental revenue adjustments which is recorded as a reduction of rental revenue and net rental accounts receivable balances. These adjustments result from contractual adjustments, audit adjustments, untimely claims filings, or billings not paid due to another provider performing same or similar functions for the patient in the same period, all of which prevent billed revenue from becoming realizable. The reserve is based on historical revenue adjustments as a percentage of rental revenue billed and unbilled during the related period. When recording the allowance for doubtful accounts, the bad debt expense account (general and administrative expense account) is charged; when recording allowance for sales returns, the sales returns account (contra sales revenue account) is charged; and when recording the allowance for rental reserve adjustments, the rental revenue adjustments account (contra rental revenue account) is charged. As of December 31, 2018 and December 31, 2017, included in accounts receivable on the consolidated balance sheets were earned but unbilled receivables of $589 and $1,470, respectively. These balances reflect gross unbilled receivables prior to any allowances for adjustments and write-offs. The Company consistently applies its allowance estimation methodology from period-to-period. The Company’s best estimate is made on an accrual basis and adjusted in future periods as required. Any adjustments to the prior period estimates are included in the current period. As additional information becomes known, the Company adjusts its assumptions accordingly to change its estimate of the allowance. For the years ended December 31, 2018 and December 31, 2017, the Company had increases of $1,757 and $3,442, respectively, in the provision for bad debt and revenue adjustments related to prior years. Gross accounts receivable balance concentrations by major category as of December 31, 2018 and December 31, 2017 were as follows: As of As of (amounts in thousands) December 31, 2018 December 31, 2017 Gross accounts receivable $ % $ % Rental (1) $ 3,406 8.7 % $ 6,236 18.0 % Business-to-business and other receivables (2) 35,656 91.3 % 28,474 82.0 % Total gross accounts receivable $ 39,062 100.0 % $ 34,710 100.0 % Net accounts receivable (gross accounts receivable, net of allowances) balance concentrations by major category as of December 31, 2018 and December 31, 2017 were as follows: As of As of (amounts in thousands) December 31, 2018 December 31, 2017 Net accounts receivable $ % $ % Rental (1) $ 2,413 6.5 % $ 4,212 13.4 % Business-to-business and other receivables (2) 34,628 93.5 % 27,232 86.6 % Total net accounts receivable $ 37,041 100.0 % $ 31,444 100.0 % (1) Rental includes Medicare, Medicaid/other government, private insurance and patient pay. ( 2 ) Business-to business receivables included one customer with a gross accounts receivable balance of $16,198 and $10,394 as of December 31, 2018 and December 31, 2017, respectively. This customer received extended payment terms through a direct financing plan offered. The Company also has a credit insurance policy in place, which allocated up to $18,000 in coverage as of December 31, 2018 and allocated up to $12,000 in coverage as of December 31, 2017 for this customer with a $400 deductible and 10% retention. The following table sets forth the percentage breakdown of the Company’s net accounts receivable (gross accounts receivable net of allowances) by aging category by invoice due date as of December 31, 2018 and December 31, 2017. As of As of (amounts in thousands) December 31, 2018 December 31, 2017 Net accounts receivable by aging category $ % $ % Held and Unbilled $ 80 0.2 % $ 537 1.7 % Aged 0-90 days 36,245 97.9 % 29,237 93.0 % Aged 91-180 days 425 1.1 % 435 1.4 % Aged 181-365 days 234 0.6 % 602 1.9 % Aged over 365 days 57 0.2 % 633 2.0 % Total net accounts receivable $ 37,041 100.0 % $ 31,444 100.0 % The following table sets forth the accounts receivable allowances as of December 31, 2018 and December 31, 2017: As of As of (amounts in thousands) December 31, 2018 December 31, 2017 Allowances - accounts receivable $ % $ % Doubtful accounts $ 693 1.8 % $ 1,415 4.1 % Rental revenue adjustments 438 1.1 % 947 2.7 % Sales returns 890 2.3 % 904 2.6 % Total allowances - accounts receivable $ 2,021 5.2 % $ 3,266 9.4 %
Concentration of Credit Risk	Concentration of credit risk Financial instruments that potentially subject the Company to concentration of credit risk consist principally of cash, cash equivalents, marketable securities and accounts receivable. At times, cash account balances may be in excess of the amounts insured by the Federal Deposit Insurance Corporation (FDIC). However, management believes the risk of loss to be minimal. The Company performs periodic evaluations of the relative credit standing of these institutions and has not experienced any losses on its cash and cash equivalents to date. The Company has also entered into hedging relationships with a single counterparty to offset the forecasted Euro-based revenues. The credit risk has been reduced due to a net settlement arrangement whereby the Company is allowed to net settle transactions with a single net amount payable by one party to the other.
Concentration of Customers and Vendors	Concentration of customers and vendors The Company primarily sells its products to traditional home medical equipment providers, distributors, and resellers in the United States and in foreign countries on a credit basis. The Company also sells its products direct-to-consumers on a primarily prepayment basis. One single customer represented more than 10% of the Company’s total revenue for the years ended December 31, 2018, 2017, and 2016. Two customers represented more than 10% of the Company’s net accounts receivable balance with accounts receivable balances of $16,198 and $4,155, respectively, as of December 31, 2018, and $10,394 and $6,459, respectively, as of December 31, 2017. The Company also rents products direct-to-consumers for insurance reimbursement, which resulted in a customer concentration relating to Medicare’s service reimbursement programs in 2016. Medicare’s service reimbursement programs accounted for 72.6% of rental revenue in the year ended December 31, 2016 and based on total revenue was 12.4% for the year ended December 31, 2016. Medicare did not represent more than 10% of the Company’s total revenue in the years ended December 31, 2018 and 2017. Medicare did not represent more than 10% of the Company’s net accounts receivable balance as of December 31, 2018 and 2017. The Company currently purchases raw materials from a limited number of vendors, which resulted in a concentration of three major vendors. The three major vendors supply the Company with raw materials used to manufacture the Company’s products. For the year ended December 31, 2018, the Company’s three major vendors accounted for 20.0%, 11.9% and 10.2%, respectively, of total raw material purchases. For the year ended December 31, 2017, the Company’s three major vendors accounted for 19.7%, 15.4% and 9.5%, respectively, of total raw material purchases. A portion of revenue is earned from sales outside the United States. Approximately 74.8% of the non-U.S. revenue for the year ended December 31, 2018 was invoiced in Euros. A breakdown of the Company’s revenue from U.S. and non-U.S. sources for the years ended December 31, 2018, 2017 and 2016 is as follows: Years ended December 31, (amounts in thousands) 2018 2017 2016 U.S. revenue $ 280,778 $ 193,919 $ 152,723 Non-U.S. revenue 77,333 55,519 50,106 Total revenue $ 358,111 $ 249,438 $ 202,829
Inventories	Inventories Inventories are stated at the lower of cost or market and net realizable value. Cost is determined using a standard cost method, including material, labor and manufacturing overhead, whereby the standard costs are updated at least quarterly to reflect approximate actual costs using the first-in, first-out (FIFO) method. The Company records adjustments at least quarterly to inventory for potentially excess, obsolete, slow-moving or impaired items. The Company recorded noncurrent inventory related to inventories that are expected to be realized or consumed after one year of $1,085 and $644 as of December 31, 2018 and 2017, respectively. Noncurrent inventories are primarily related to raw materials purchased in bulk to support long-term expected repairs to reduce costs and are classified in other assets. December 31, (amounts in thousands) 2018 2017 Raw materials and work-in-progress $ 24,980 $ 16,324 Finished goods 2,756 2,917 Less: reserves (665 ) (399 ) Inventories $ 27,071 $ 18,842
Property and Equipment	Property and equipment Property and equipment are stated at cost. Depreciation and amortization are calculated using the straight-line method over the assets’ estimated useful lives as follows: Rental equipment 1.5-5 years Manufacturing equipment and tooling 3-5 years Computer equipment and software 2-3 years Furniture and equipment 3-5 years Leasehold improvements Lesser of estimated useful life or remaining lease term Expenditures for additions, improvements and replacements are capitalized and depreciated to a salvage value of $0. Repair and maintenance costs on rental equipment are included in cost of rental revenue on the consolidated statements of comprehensive income. Repair and maintenance expense, which includes labor, parts and freight, for rental equipment was $2,289, $2,385 and $2,464 for the years ended December 31, 2018, 2017 and 2016, respectively. Included within property and equipment is construction in process, primarily related to the design and engineering of tooling, jigs and other machinery. In addition, this item also includes computer software or development costs that have been purchased but have not completed the final configuration process for implementation into the Company’s systems. These items have not been placed in service; therefore, no depreciation or amortization was recognized for these items in the respective periods. Depreciation and amortization expense related to rental equipment and other property and equipment are summarized below for the years ended December 31, 2018, 2017 and 2016, respectively. Years ended December 31, (amounts in thousands) 2018 2017 2016 Rental equipment $ 7,567 $ 9,835 $ 11,429 Other property and equipment 2,463 1,960 2,028 Total depreciation and amortization $ 10,030 $ 11,795 $ 13,457 Property and equipment and rental equipment with associated accumulated depreciation is summarized below as of December 31, 2018 and 2017, respectively. (amounts in thousands) December 31, Property and equipment 2018 2017 Rental equipment, net of allowances of $594 and $754, respectively $ 43,038 $ 49,349 Other property and equipment 21,596 15,219 Property and equipment 64,634 64,568 Accumulated depreciation Rental equipment 31,813 34,754 Other property and equipment 10,480 9,711 Accumulated depreciation 42,293 44,465 Property and equipment, net Rental equipment, net of allowances of $594 and $754, respectively 11,225 14,595 Other property and equipment 11,116 5,508 Property and equipment, net $ 22,341 $ 20,103
Long-lived Assets	Long-lived assets The Company accounts for the impairment and disposition of long-lived assets in accordance with ASC 360 — Property, Plant, and Equipment
Goodwill and Intangible Assets	Goodwill and intangible assets Goodwill is tested for impairment on an annual basis as of October 1. Interim testing of goodwill for impairment is also required whenever an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit or asset below its carrying amount. No impairments were recorded as of December 31, 2018 and 2017. Finite-lived intangible assets are amortized over their useful lives and are tested for recoverability whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. Customer relationships and non-compete agreements are amortized using the straight-line method.
Business Combinations	Business combinations The results of operations of the businesses acquired by the Company are included as of the acquisition date. The purchase price of an acquisition is allocated to the underlying assets acquired and liabilities assumed based upon their estimated fair values at the date of acquisition. To the extent the purchase price exceeds the fair value of the net identifiable tangible and intangible assets acquired and liabilities assumed, such excess is allocated to goodwill. The Company may adjust the preliminary purchase price allocation, as necessary, for up to one year after the acquisition closing date if it obtains more information regarding asset valuations and liabilities assumed. Acquisition-related expenses are recognized separately from the business combination and are expensed as incurred.
Loss Contingencies	Loss contingencies The Company is involved in various lawsuits, claims, investigations, and proceedings that arise in the ordinary course of business. The Company records a liability when it believes that it is both probable that a loss has been incurred and the amount can be reasonably estimated. Significant judgment is required to determine both probability and the estimated amount. The Company reviews at least quarterly and adjusts accordingly to reflect the impact of negotiations, settlements, rulings, advice of legal counsel, and updated information. At this time, the Company has no accrual related to lawsuits, claims, investigations and proceedings.
Deferred Rent	Deferred rent The Company’s operating leases for its office facilities in California, Texas and Ohio include a rent abatement period and scheduled rent increases. The Company has accounted for the leases to provide straight-line charges to operations over the life of the leases.
Research and Development	Research and development Research and development costs are expensed as incurred.
Advertising Costs	Advertising costs Advertising costs, which approximated $30,755, $12,511 and $6,215 during the years ended December 31, 2018, 2017 and 2016, respectively, are expensed as incurred, excluding the production costs of direct response advertising. Advertising costs are included in sales and marketing expense in the accompanying consolidated statements of comprehensive income.
Income Taxes	Income taxes The Company accounts for income taxes in accordance with ASC 740 —Income Taxes The Company accounts for uncertainties in income tax in accordance with ASC 740-10 —Accounting for Uncertainty in Income Taxes The Company recognizes interest and penalties on taxes, if any, within its income tax provision on its consolidated statements of comprehensive income. No interest or penalties were recognized during the periods presented. On December 22, 2017, the Tax Cuts and Jobs Act (TCJA) was enacted into law, which significantly changes existing U.S. tax law and includes numerous provisions that affect the Company’s business. Changes include, but are not limited to, a corporate tax rate decrease from 34% to 21% effective for tax years beginning after December 31, 2017, expensing of capital expenditures, the transition of U.S. international taxation from a worldwide tax system to a territorial system, a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings, and limitations on the deductibility of certain executive compensation and other deductions
Accounting for Stock-Based Compensation	Accounting for stock-based compensation The Company accounts for its stock-based compensation in accordance with ASC 718 —Compensation—Stock Compensation As part of the provisions of ASC 718, the Company is required to estimate potential forfeitures of stock grants and adjust compensation cost recorded accordingly. The estimate of forfeitures will be adjusted over the requisite service period to the extent that actual forfeitures differ, or are expected to differ, from such estimates. Changes in estimated forfeitures will be recognized through a cumulative catch-up adjustment in the period of change and will also impact the amount of stock compensation expense to be recognized in future periods.
Foreign Currency	Foreign currency The functional currency of the Company’s international subsidiaries is the local currency. The financial statements of the subsidiaries are translated to U.S. dollars using month-end exchange rates for assets and liabilities, and average rates of exchange for revenues, cost of revenue, operating expense and provision for income taxes. Translation gains and losses are recorded in accumulated other comprehensive income (loss) as a component of stockholders’ equity. Foreign exchange transaction gains and losses resulting from the conversion of the transaction currency to functional currency are reflected as a component of foreign currency exchange gains or losses in other income (expense) in the consolidated statements of comprehensive income.
Business Segments	Business segments The Company operates and reports in only one operating and reportable segment – development, manufacturing, marketing, sales, and rental of respiratory products. Management reports financial information on a consolidated basis to the Company’s chief operating decision maker.
Earnings Per Share	Earnings per share Earnings per share (EPS) is computed in accordance with ASC 260 —Earnings per Share Basic earnings per share is calculated using the Company’s weighted-average outstanding common shares. Diluted earnings per share is calculated using the Company’s weighted-average outstanding common shares including the dilutive effect of stock awards as determined under the treasury stock method. The computation of EPS is as follows: Years ended December 31, (amounts in thousands, except share and per share amounts) 2018 2017 2016 Numerator—basic and diluted: Net income $ 51,845 $ 21,002 $ 20,519 Denominator: Weighted-average common shares - basic common stock (1) 21,266,696 20,683,807 20,067,152 Weighted-average common shares - diluted common stock 22,514,513 21,897,988 21,095,867 Net income per share - basic common stock $ 2.44 $ 1.02 $ 1.02 Net income per share - diluted common stock $ 2.30 $ 0.96 $ 0.97 Denominator calculation from basic to diluted: Weighted-average common shares - basic common stock (1) 21,266,696 20,683,807 20,067,152 Stock options and other dilutive awards 1,247,817 1,214,181 1,028,715 Weighted-average common shares - diluted common stock 22,514,513 21,897,988 21,095,867 Shares excluded from diluted weighted-average shares: Stock options — 37,249 841,760 Restricted stock units and restricted stock awards 39,330 26,064 — Shares excluded from diluted weighted-average shares 39,330 63,313 841,760 (1) Unvested restricted stock units and restricted stock awards are not included as shares outstanding in the calculation of basic earnings per share. Vested restricted stock units and restricted stock awards are included in basic earnings per share if all vesting and performance criteria have been met. Performance-based restricted stock units and restricted stock awards are included in the number of shares used to calculate diluted earnings per share as long as all applicable performance criteria are met, and their effect is dilutive. Restricted stock awards are eligible to receive all dividends declared on the Company’s common shares during the vesting period; however, such dividends are not paid until the restrictions lapse. The computations of diluted net income attributable to common stockholders excluded common stock options, restricted stock units, and restricted stock awards, which were anti-dilutive for the years ended December 31, 2018, 2017 and 2016.
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently issued accounting pronouncements not yet adopted In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-02, Leases (Topic 842) Land Easement Practice Expedient for Transition to Topic 842 In June 2016, the FASB issued ASU No. 2016-13, Accounting for Credit Losses (Topic 326) In January 2017, the FASB issued ASU No. 2017-04, Simplifying the Test for Goodwill Impairment In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging In January 2018, the FASB issued ASU No. 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income In June 2018, the FASB issued ASU No. 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement In November 2018, the FASB issued ASU No. 2018-19, Codification Improvements to Topic 326, Financial Instruments-Credit Losses
Recently Adopted Accounting Pronouncements	Recently adopted accounting pronouncements In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers Revenue with Contracts with Customers: Principal versus Agent Considerations (Reporting Revenue Gross versus Net) In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities In January 2017, the FASB issued ASU No. 2017-01, Clarifying the Definition of a Business In August 2018, the FASB issued ASU No. 2018-15, Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Sales Revenue Disaggregated by Sales Channel and Geographic Region	The following table sets forth the Company’s sales revenue disaggregated by sales channel and geographic region: (amounts in thousands) Years ended December 31, Revenue by region and category 2018 2017 2016 Business-to-business domestic sales $ 116,581 $ 83,390 $ 56,605 Business-to-business international sales 77,333 55,519 50,106 Direct-to-consumer domestic sales 142,101 86,583 61,459 Total sales revenue $ 336,015 $ 225,492 $ 168,170
Summary of Fair Value Assets Measured on Recurring Basis for Cash, Cash Equivalents and Marketable Securities	The following table summarizes fair value measurements by level for the assets measured at fair value on a recurring basis for cash, cash equivalents and marketable securities: As of December 31, 2018 Gross Cash Adjusted unrealized and cash Marketable (amounts in thousands) cost gains (losses) Fair value equivalents securities Cash $ 33,671 $ — $ 33,671 $ 33,671 $ — Level 1: Money market accounts 158,438 — 158,438 158,438 — Level 2: Corporate bonds 13,629 (16 ) 13,613 — 13,613 U.S. Treasury securities 34,620 7 34,627 4,525 30,102 Total $ 240,358 $ (9 ) $ 240,349 $ 196,634 $ 43,715 As of December 31, 2017 Gross Cash Adjusted unrealized and cash Marketable (amounts in thousands) cost losses Fair value equivalents securities Cash $ 46,237 $ — $ 46,237 $ 46,237 $ — Level 1: Money market accounts 93,430 — 93,430 93,430 — Level 2: Certificates of deposit 11,010 (4 ) 11,006 490 10,516 Corporate bonds 20,789 (21 ) 20,768 2,796 17,972 Agency mortgage-backed securities 2,005 (1 ) 2,004 — 2,004 U.S. Treasury securities 499 — 499 — 499 Total $ 173,970 $ (26 ) $ 173,944 $ 142,953 $ 30,991
Summary of Estimated Fair Value of Company's Investments in Marketable Securities Classified by Contractual Maturity Date	The following table summarizes the estimated fair value of the Company’s investments in marketable securities, classified by the contractual maturity date of the securities: December 31, (amounts in thousands) 2018 Due within one year $ 43,715 Due in one year through five years — Total $ 43,715
Summary of Components of Accumulated Other Comprehensive Income (Loss)	The components of accumulated other comprehensive income (loss) were as follows: As of December 31, 2018 Foreign Unrealized Unrealized Accumulated currency gains (losses) on gains (losses) other translation marketable on cash comprehensive (amounts in thousands) adjustments securities flow hedges income Balance as of December 31, 2017 $ 363 $ (17 ) $ (74 ) $ 272 Other comprehensive gain 31 17 404 452 Balance as of December 31, 2018 $ 394 $ — $ 330 $ 724 As of December 31, 2017 Foreign Unrealized Unrealized Accumulated currency gains (losses) on gains (losses) other translation marketable on cash comprehensive (amounts in thousands) adjustments securities flow hedges income (loss) Balance as of December 31, 2016 $ — $ (82 ) $ 47 $ (35 ) Other comprehensive gain (loss) 363 65 (121 ) 307 Balance as of December 31, 2017 $ 363 $ (17 ) $ (74 ) $ 272
Summary of Cash, Cash Equivalents and Short-term Investments	. Cash, cash equivalents, and marketable securities consist of the following: (amounts in thousands) December 31, Cash and cash equivalents 2018 2017 Cash $ 33,671 $ 46,237 Money market accounts 158,438 93,430 Certificates of deposit — 490 Corporate bonds — 2,796 U.S. Treasury securities 4,525 — Total cash and cash equivalents $ 196,634 $ 142,953 Marketable securities Certificates of deposit $ — $ 10,516 Corporate bonds 13,613 17,972 Agency mortgage-backed securities — 2,004 U. S. Treasury securities 30,102 499 Total marketable securities $ 43,715 $ 30,991
Schedule of Gross Accounts Receivable Balance Concentrations by Major Category	Gross accounts receivable balance concentrations by major category as of December 31, 2018 and December 31, 2017 were as follows: As of As of (amounts in thousands) December 31, 2018 December 31, 2017 Gross accounts receivable $ % $ % Rental (1) $ 3,406 8.7 % $ 6,236 18.0 % Business-to-business and other receivables (2) 35,656 91.3 % 28,474 82.0 % Total gross accounts receivable $ 39,062 100.0 % $ 34,710 100.0 %
Schedule of Net Accounts Receivable Balance Concentrations by Major Category	Net accounts receivable (gross accounts receivable, net of allowances) balance concentrations by major category as of December 31, 2018 and December 31, 2017 were as follows: As of As of (amounts in thousands) December 31, 2018 December 31, 2017 Net accounts receivable $ % $ % Rental (1) $ 2,413 6.5 % $ 4,212 13.4 % Business-to-business and other receivables (2) 34,628 93.5 % 27,232 86.6 % Total net accounts receivable $ 37,041 100.0 % $ 31,444 100.0 % (1) Rental includes Medicare, Medicaid/other government, private insurance and patient pay. ( 2 ) Business-to business receivables included one customer with a gross accounts receivable balance of $16,198 and $10,394 as of December 31, 2018 and December 31, 2017, respectively. This customer received extended payment terms through a direct financing plan offered. The Company also has a credit insurance policy in place, which allocated up to $18,000 in coverage as of December 31, 2018 and allocated up to $12,000 in coverage as of December 31, 2017 for this customer with a $400 deductible and 10% retention.
Schedule of Percentage Breakdown of Net Accounts Receivable by Aging Category by Invoice Due Date	The following table sets forth the percentage breakdown of the Company’s net accounts receivable (gross accounts receivable net of allowances) by aging category by invoice due date as of December 31, 2018 and December 31, 2017. As of As of (amounts in thousands) December 31, 2018 December 31, 2017 Net accounts receivable by aging category $ % $ % Held and Unbilled $ 80 0.2 % $ 537 1.7 % Aged 0-90 days 36,245 97.9 % 29,237 93.0 % Aged 91-180 days 425 1.1 % 435 1.4 % Aged 181-365 days 234 0.6 % 602 1.9 % Aged over 365 days 57 0.2 % 633 2.0 % Total net accounts receivable $ 37,041 100.0 % $ 31,444 100.0 %
Schedule of Allowances for Accounts Receivable	The following table sets forth the accounts receivable allowances as of December 31, 2018 and December 31, 2017: As of As of (amounts in thousands) December 31, 2018 December 31, 2017 Allowances - accounts receivable $ % $ % Doubtful accounts $ 693 1.8 % $ 1,415 4.1 % Rental revenue adjustments 438 1.1 % 947 2.7 % Sales returns 890 2.3 % 904 2.6 % Total allowances - accounts receivable $ 2,021 5.2 % $ 3,266 9.4 %
Breakdown of Company's Revenue from U.S. and Non-U.S. Sources	A portion of revenue is earned from sales outside the United States. Approximately 74.8% of the non-U.S. revenue for the year ended December 31, 2018 was invoiced in Euros. A breakdown of the Company’s revenue from U.S. and non-U.S. sources for the years ended December 31, 2018, 2017 and 2016 is as follows: Years ended December 31, (amounts in thousands) 2018 2017 2016 U.S. revenue $ 280,778 $ 193,919 $ 152,723 Non-U.S. revenue 77,333 55,519 50,106 Total revenue $ 358,111 $ 249,438 $ 202,829
Schedule of Inventories	Inventories that are considered current consist of the following: December 31, (amounts in thousands) 2018 2017 Raw materials and work-in-progress $ 24,980 $ 16,324 Finished goods 2,756 2,917 Less: reserves (665 ) (399 ) Inventories $ 27,071 $ 18,842
Computation of Depreciation and Amortization using Straight Line Method Over Estimated Useful Lives of Assets	Property and equipment are stated at cost. Depreciation and amortization are calculated using the straight-line method over the assets’ estimated useful lives as follows: Rental equipment 1.5-5 years Manufacturing equipment and tooling 3-5 years Computer equipment and software 2-3 years Furniture and equipment 3-5 years Leasehold improvements Lesser of estimated useful life or remaining lease term
Summary of Depreciation and Amortization Expense of Rental Equipment and Other Property and Equipment	Depreciation and amortization expense related to rental equipment and other property and equipment are summarized below for the years ended December 31, 2018, 2017 and 2016, respectively. Years ended December 31, (amounts in thousands) 2018 2017 2016 Rental equipment $ 7,567 $ 9,835 $ 11,429 Other property and equipment 2,463 1,960 2,028 Total depreciation and amortization $ 10,030 $ 11,795 $ 13,457
Summary of Property Plant and Equipment and Rental Equipment with Associated Accumulated Depreciation	Property and equipment and rental equipment with associated accumulated depreciation is summarized below as of December 31, 2018 and 2017, respectively. (amounts in thousands) December 31, Property and equipment 2018 2017 Rental equipment, net of allowances of $594 and $754, respectively $ 43,038 $ 49,349 Other property and equipment 21,596 15,219 Property and equipment 64,634 64,568 Accumulated depreciation Rental equipment 31,813 34,754 Other property and equipment 10,480 9,711 Accumulated depreciation 42,293 44,465 Property and equipment, net Rental equipment, net of allowances of $594 and $754, respectively 11,225 14,595 Other property and equipment 11,116 5,508 Property and equipment, net $ 22,341 $ 20,103
Computation of Earnings Per Share	The computation of EPS is as follows: Years ended December 31, (amounts in thousands, except share and per share amounts) 2018 2017 2016 Numerator—basic and diluted: Net income $ 51,845 $ 21,002 $ 20,519 Denominator: Weighted-average common shares - basic common stock (1) 21,266,696 20,683,807 20,067,152 Weighted-average common shares - diluted common stock 22,514,513 21,897,988 21,095,867 Net income per share - basic common stock $ 2.44 $ 1.02 $ 1.02 Net income per share - diluted common stock $ 2.30 $ 0.96 $ 0.97 Denominator calculation from basic to diluted: Weighted-average common shares - basic common stock (1) 21,266,696 20,683,807 20,067,152 Stock options and other dilutive awards 1,247,817 1,214,181 1,028,715 Weighted-average common shares - diluted common stock 22,514,513 21,897,988 21,095,867 Shares excluded from diluted weighted-average shares: Stock options — 37,249 841,760 Restricted stock units and restricted stock awards 39,330 26,064 — Shares excluded from diluted weighted-average shares 39,330 63,313 841,760 (1) Unvested restricted stock units and restricted stock awards are not included as shares outstanding in the calculation of basic earnings per share. Vested restricted stock units and restricted stock awards are included in basic earnings per share if all vesting and performance criteria have been met. Performance-based restricted stock units and restricted stock awards are included in the number of shares used to calculate diluted earnings per share as long as all applicable performance criteria are met, and their effect is dilutive. Restricted stock awards are eligible to receive all dividends declared on the Company’s common shares during the vesting period; however, such dividends are not paid until the restrictions lapse.

Goodwill and Other Identifiab_2

Goodwill and Other Identifiable Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Schedule of Changes in Carrying Amount of Goodwill	The changes in the carrying amount of goodwill for the years ended December 31, 2018 and 2017 were as follows: (amounts in thousands) Balance as of December 31, 2016 $ — Acquisition 2,154 Translation adjustment 209 Balance as of December 31, 2017 $ 2,363 Translation adjustment (106 ) Balance as of December 31, 2018 $ 2,257
Summary of Intangible Assets	The following tables represent the changes in net carrying values of the intangibles as of the respective dates: Average estimated Gross (amounts in thousands) useful lives carrying Accumulated December 31, 2018 (in years) amount amortization Net amount Licenses 10 $ 185 $ 155 $ 30 Patents and websites 5 4,164 1,640 2,524 Customer relationships 4 1,373 572 801 Non-compete agreement 2.3 229 154 75 Commercials 2-3 633 308 325 Total $ 6,584 $ 2,829 $ 3,755 Average estimated Gross (amounts in thousands) useful lives carrying Accumulated December 31, 2017 (in years) amount amortization Net amount Licenses 10 $ 185 $ 137 $ 48 Patents and websites 5 4,173 959 3,214 Customer relationships 4 1,437 240 1,197 Non-compete agreement 3 240 52 188 Commercials 2-3 303 233 70 Total $ 6,338 $ 1,621 $ 4,717
Schedule of Annual Estimated Amortization Expense	Annual estimated amortization expense for each of the succeeding fiscal years is as follows: (amounts in thousands) Intangible Years ending December 31, amortization 2019 $ 1,234 2020 1,132 2021 844 2022 545 2023 — Thereafter — Total $ 3,755

Current Liabilities (Tables)

Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
Payables And Accruals [Abstract]
Schedule of Accounts Payable and Accrued Expenses	Accounts payable and accrued expenses as of December 31, 2018 and 2017 consisted of the following: December 31, (amounts in thousands) 2018 2017 Accounts payable $ 13,720 $ 9,541 Accrued inventory (in-transit and unvouchered receipts) and trade payables 9,597 7,252 Accrued purchasing card liability 2,089 2,381 Accrued franchise, sales and use taxes 518 479 Other accrued expenses 862 973 Accounts payable and accrued expenses $ 26,786 $ 20,626
Schedule of Accrued Payroll	Accrued payroll as of December 31, 2018 and 2017 consisted of the following: December 31, (amounts in thousands) 2018 2017 Accrued bonuses $ 4,780 $ 3,086 Accrued wages and other payroll related items 3,494 1,746 Accrued vacation 1,959 1,338 Accrued employee stock purchase plan deductions 1,174 707 Accrued payroll $ 11,407 $ 6,877

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Components of Income Before Provision for Income Taxes	The components of the Company’s income before provision for income taxes are as follows: Years ended December 31, (amounts in thousands) 2018 2017 2016 United States $ 40,245 $ 29,121 $ 22,725 Foreign 210 535 — Income before provision for income taxes $ 40,455 $ 29,656 $ 22,725
Components of Provisions for Income Taxes	The provision for income taxes consists of the following: Years ended December 31, (amounts in thousands) 2018 2017 2016 Current tax expense (benefit) Federal $ — $ 245 $ 451 State (40 ) 240 776 Foreign 171 206 — Total current tax expense 131 691 1,227 Deferred tax expense (benefit) Federal (9,774 ) 8,709 1,357 State (1,630 ) 92 590 Foreign (117 ) (71 ) — Total deferred tax expense (benefit) (11,521 ) 8,730 1,947 Tax benefit for change in valuation allowance — (767 ) (968 ) Total deferred tax expense (benefit), net (11,521 ) 7,963 979 Income tax expense (benefit) $ (11,390 ) $ 8,654 $ 2,206
Components of Deferred Tax Assets and Liabilities	The components of deferred tax assets and liabilities consist of the following: As of December 31, (amounts in thousands) 2018 2017 Deferred tax assets (liabilities) Accrued expenses $ 8,033 $ 5,669 Net operating loss and credit carryforward 19,805 10,378 Allowance, reserves and other 3,490 3,301 Stock-based compensation 3,253 2,598 Deferred tax assets 34,581 21,946 Property, plant, and equipment (4,683 ) (3,658 ) Total $ 29,898 $ 18,288
Reconciliation of the Federal Statutory Income Tax Rate to the Effective Income Tax Rate	Reconciliation of the federal statutory income tax rate to the effective income tax rate for the last three years is as follows: Years ended December 31, 2018 2017 2016 U.S. Statutory rate 21.00 % 34.00 % 34.00 % State income taxes, net of federal benefit (3.73 ) 0.37 0.88 Stock-based compensation (45.01 ) (30.40 ) (23.74 ) Change in valuation allowance — (2.59 ) (4.26 ) R&D credit, net of reserve (1.39 ) (1.43 ) (1.75 ) Expiration of net operating losses — 2.76 4.51 Effect of U.S tax law change — 25.55 — Other 0.98 0.92 0.07 Effective income tax rate (28.15)% 29.18 % 9.71 %
Summary of Reconciliation of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefit is as follows: December 31, (amounts in thousands) 2018 2017 2016 Reconciliation of liability for unrecognized tax benefits Balance at beginning of period $ 1,062 $ 934 $ 773 Additions based on tax positions related to current year 232 128 161 Balance at end of period $ 1,294 $ 1,062 $ 934

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Summary of Stock Options Activity	The activity for stock options under the Company’s stock plans is as follows: Remaining weighted- Weighted- average Per share average contractual average Price per exercise terms intrinsic Options share price (in years) value Outstanding as of December 31, 2015 2,295,370 $0.60-$46.66 $ 19.36 5.98 $ 21.07 Granted 683,998 44.19-58.95 44.70 Exercised (570,079 ) 0.60-46.66 12.32 Forfeited (53,247 ) 1.17-44.19 28.09 Expired (515 ) 8.70 8.70 Outstanding as of December 31, 2016 2,355,527 0.60-58.95 28.22 5.42 38.95 Vested and exercisable as of December 31, 2016 1,023,865 0.60-46.66 16.61 4.96 50.56 Vested and expected to vest as of December 31, 2016 2,259,811 0.60-46.66 27.95 5.40 39.22 Outstanding as of December 31, 2016 2,355,527 0.60-58.95 28.22 5.42 38.95 Granted 64,498 83.30 83.30 Exercised (520,393 ) 0.60-58.95 24.16 Forfeited (63,173 ) 24.52-58.95 43.74 Expired (33 ) 8.70 8.70 Outstanding as of December 31, 2017 1,836,426 0.60-83.30 30.77 4.58 88.31 Vested and exercisable as of December 31, 2017 1,176,504 0.60-83.30 24.33 4.39 94.75 Vested and expected to vest as of December 31, 2017 1,792,871 0.60-83.30 30.50 4.58 88.58 Outstanding as of December 31, 2017 1,836,426 0.60-83.30 30.77 4.58 88.31 Granted — — — Exercised (708,319 ) 0.60-58.95 24.22 Forfeited (771 ) 24.52-44.19 28.24 Expired — — — Outstanding as of December 31, 2018 1,127,336 0.75-83.30 34.89 3.84 89.28 Vested and exercisable as of December 31, 2018 851,039 0.75-83.30 32.12 3.75 92.05 Vested and expected to vest as of December 31, 2018 1,109,280 $0.75-$83.30 $ 34.75 3.84 $ 89.42
Summary of Restricted Stock Activity	Stock Awards activity for the years ended December 31, 2018 and December 31, 2017 are summarized below: Weighted- average grant Performance date fair and value Time-based time-based Total per share Unvested restricted stock units as of December 31, 2016 — — — $ — Granted 42,028 13,109 55,137 90.05 Vested — — — — Forfeited/canceled — — — — Unvested restricted stock units as of December 31, 2017 (1) 42,028 13,109 55,137 $ 90.05 Unvested and expected to vest restricted stock units outstanding as of December 31, 2017 48,589 $ 89.95 Unvested restricted stock units as of December 31, 2017 42,028 13,109 55,137 $ 90.05 Granted 31,877 — 31,877 143.50 Vested (13,742 ) (4,370 ) (18,112 ) 89.35 Forfeited/canceled (1,574 ) — (1,574 ) 106.55 Unvested restricted stock units as of December 31, 2018 (1) 58,589 8,739 67,328 $ 115.16 Unvested and expected to vest restricted stock units outstanding as of December 31, 2018 62,504 $ 115.98 Unvested restricted stock awards outstanding as of December 31, 2016 — — — $ — Granted 20,789 20,785 41,574 91.52 Vested — — — — Forfeited/canceled — — — — Unvested restricted stock awards outstanding as of December 31, 2017 (1) 20,789 20,785 41,574 $ 91.52 Unvested and expected to vest restricted stock awards outstanding as of December 31, 2017 34,051 $ 91.52 Unvested restricted stock awards outstanding as of December 31, 2017 20,789 20,785 41,574 $ 91.52 Granted 22,645 33,964 56,609 130.89 Vested (6,497 ) (6,928 ) (13,425 ) 91.52 Forfeited/canceled — — — — Unvested restricted stock awards outstanding as of December 31, 2018 (1) 36,937 47,821 84,758 $ 115.80 Unvested and expected to vest restricted stock awards outstanding as of December 31, 2018 65,773 $ 115.85 (1 ) Outstanding restricted stock units and restricted stock awards are based on the maximum payout of the targeted number of shares.
Summary of Stock-based Compensation Expense	Stock-based compensation Stock-based compensation expense recognized for the years ended December 31, 2018, 2017 and 2016 was as follows: Years ended December 31, (amounts in thousands) 2018 2017 2016 Stock-based compensation expense by type of award: Stock option plan awards $ 6,015 $ 7,652 $ 6,850 Restricted stock units and restricted stock awards 5,890 1,447 — Employee stock purchase plan 885 541 444 Total stock-based compensation expense $ 12,790 $ 9,640 $ 7,294 For the years ended December 31, 2018, 2017 and 2016, stock-based compensation expense recognized under ASC 718, included in cost of revenues, sales and marketing expense, general and administrative expense, and research and development expense was as follows: Years ended December 31, (amounts in thousands) 2018 2017 2016 Cost of revenue $ 1,060 $ 845 $ 639 Research and development 1,314 1,015 776 Sales and marketing 2,355 1,558 1,142 General and administrative 8,061 6,222 4,737 Total stock-based compensation expense $ 12,790 $ 9,640 $ 7,294
Assumptions Applied to Estimate Fair Value of Stock Option Awards	The following table displays the assumptions that have been applied to estimate the fair value of stock option awards on the date of grant using the Black-Scholes option pricing model. During 2018, the Company did not grant any stock option awards. 2017 2016 Expected term (years) 3.54-4.00 3.54-5.48 Risk free interest rate 1.65-1.73% 1.00-1.40% Expected dividend yield None None Volatility 41.61-42.15% 43.95-45.93%
Assumptions Applied to Estimate Fair Value of Shares Issued Under ESPP	The following table displays the assumptions that have been applied to estimate the fair value of the Company’s shares to be issued under the ESPP using the Black-Scholes option pricing model. 2018 2017 2016 Expected term (years) 0.50 0.50 0.50 Risk free interest rate 1.63-2.46% 1.15-1.63% 1.15-1.32% Expected dividend yield None None None Volatility 37.34-44.00% 42.35-45.34% 43.28-44.81%

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Minimum Aggregate Payments Due under Operating Leases and Specified Non-Cancelable Contractual Obligations Consist of Software License and Maintenance Agreements	The Company leases its facilities and certain equipment under operating leases that expire through September 2024. At December 31, 2018, the minimum aggregate payments due under operating leases and specified non-cancelable contractual obligations, which consist of software license and maintenance agreements, Non-cancelable Operating Related party contractual (amounts in thousands) leases leases obligations Total 2019 $ 2,450 $ 31 $ 578 $ 3,059 2020 2,212 10 578 2,800 2021 1,593 — 457 2,050 2022 1,273 — — 1,273 2023 1,215 — — 1,215 Thereafter 917 — — 917 Total $ 9,660 $ 41 $ 1,613 $ 11,314
Schedule of Changes in Aggregate Product Warranty Liabilities	The following table identifies the changes in the Company’s aggregate product warranty liabilities for the years ended December 31, 2018, 2017 and 2016: December 31, (amounts in thousands) 2018 2017 2016 Product warranty liability at beginning of period $ 6,171 $ 3,480 $ 1,973 Accruals for warranties issued 7,693 5,275 3,123 Adjustments related to preexisting warranties (including changes in estimates) 90 200 118 Settlements made (in cash or in kind) (4,424 ) (2,784 ) (1,734 ) Product warranty liability at end of period $ 9,530 $ 6,171 $ 3,480

Quarterly Summary of Informat_2

Quarterly Summary of Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Summary of Unaudited Quarterly Statements of Income Data	The following table sets forth the Company’s unaudited quarterly statements of income data in dollars for each of the eight quarters in the period ended December 31, 2018. The Company has prepared the quarterly statements of income data on a basis consistent with the audited financial statements. In the opinion of management, the financial information reflects all adjustments, consisting only of normal recurring adjustments, which the Company considers necessary for a fair presentation of this data. The results of historical periods are not necessarily indicative of the results of operations for any future period. (amounts in thousands, except share and per share amounts) Quarterly Results 2018 Q1 March Q2 June Q3 September Q4 December Total revenue $ 79,051 $ 97,238 $ 95,291 $ 86,531 Gross profit 37,727 48,470 48,813 43,570 Income before benefit for income taxes 9,687 13,646 11,299 5,823 Benefit for income taxes (1,071 ) (964 ) (5,133 ) (4,222 ) Net income 10,758 14,610 16,432 10,045 Net income per share attributable to common stockholders: Basic $ 0.51 $ 0.69 $ 0.77 $ 0.47 Diluted $ 0.48 $ 0.65 $ 0.73 $ 0.44 Weighted-average number of shares used in calculating net income per share attributable to common stockholders: Basic common shares 21,026,154 21,172,170 21,324,256 21,544,202 Diluted common shares 22,295,213 22,503,749 22,659,052 22,600,038 (amounts in thousands, except share and per share amounts) Quarterly Results 2017 Q1 March Q2 June Q3 September Q4 December Total revenue $ 52,500 $ 64,121 $ 69,030 $ 63,787 Gross profit 25,744 31,567 33,170 30,756 Income before provision (benefit) for income taxes 5,879 9,166 8,817 5,794 Provision (benefit) for income taxes (53 ) 828 1,479 6,400 Net income (loss) 5,932 8,338 7,338 (606 ) Net income (loss) per share attributable to common stockholders: Basic $ 0.29 $ 0.40 $ 0.35 $ (0.03 ) Diluted $ 0.27 $ 0.38 $ 0.33 $ (0.03 ) Weighted-average number of shares used in calculating net income (loss) per share attributable to common stockholders: Basic common shares 20,489,532 20,622,320 20,753,789 20,869,589 Diluted common shares 21,579,721 21,848,359 21,998,660 22,167,358

Nature of Business - Additional

Nature of Business - Additional Information (Details) $ in Thousands	May 04, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2018USD ($)Product	Dec. 31, 2017USD ($)
Nature Of Business [Line Items]
Goodwill acquired		$ 2,363	$ 2,257	$ 2,363
MedSupport Systems B.V.
Nature Of Business [Line Items]
Aggregate payment for acquisition	$ 5,831
Cash paid at closing	5,779
Net working capital adjustments paid		$ 52
Cash acquired	1,337
Intangible assets acquired	1,529
Goodwill acquired	2,154
Net assets assumed	$ 811
MedSupport Systems B.V. | General and Administrative
Nature Of Business [Line Items]
Acquisition expenses				$ 370
Inogen Europe Holding B.V.
Nature Of Business [Line Items]
Date of incorporation of subsidiary			Apr. 13, 2017
Europe Holding B V And Inogen Europe B V
Nature Of Business [Line Items]
Effective date of merger			Dec. 28, 2018
Inogen One | Minimum
Nature Of Business [Line Items]
Number of portable oxygen concentrators | Product			567,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2018USD ($)CustomerSegment	Dec. 31, 2017USD ($)Customer	Dec. 31, 2016USD ($)Customer
Significant Accounting Policies [Line Items]
Standard warranty period offered		3 years
Cash payments received in advance of satisfying performance obligations		$ 6,909,000	$ 4,290,000
Performance obligation partially offset of revenue recognized	$ 752,000	2,855,000	752,000
Deferred capped rental revenue	0	$ 0	0
Rental revenue earned		30 days
Accounts receivable, net	31,444,000	$ 37,041,000	31,444,000
Unbilled Receivables	1,470,000	589,000	1,470,000
Increase in provision for bad debt and revenue adjustments related to prior years		$ 1,757,000	3,442,000
Percentage of Non-US revenue invoiced in Euros		74.80%
Transfer of inventory to rental equipment		$ 1,187,000	1,055,000	$ 1,454,000
Salvage value of expenditures for additions, improvements and replacements		0
Repairs and maintenance expense		2,289,000	2,385,000	2,464,000
Depreciation and amortization		10,030,000	11,795,000	13,457,000
Impairments of long-lived assets		0	0
Goodwill impairment loss		0	0
Advertising costs		30,755,000	12,511,000	6,215,000
Unrecognized tax benefits, interest or penalties recognized		$ 0	$ 0	$ 0
Corporate tax rate		21.00%	34.00%	34.00%
Provision for income taxes related TCJA	7,578,000
Additional adjustment to provisional amount related to TCJA	0
Number of operating segments | Segment		1
Number of reportable segments | Segment		1
ASU 2016-02
Significant Accounting Policies [Line Items]
Operating lease, right-of-use asset		$ 6,400,000
Operating lease, liability		6,400,000
Construction in Process and Computer Software or Development Cost
Significant Accounting Policies [Line Items]
Depreciation and amortization		0	$ 0	$ 0
Other Noncurrent Assets
Significant Accounting Policies [Line Items]
Noncurrent inventories expected to be realized or consumed	644,000	1,085,000	644,000
Customer Concentration Risk | Customer One
Significant Accounting Policies [Line Items]
Accounts receivable, net	10,394,000	16,198,000	10,394,000
Customer Concentration Risk | Customer Two
Significant Accounting Policies [Line Items]
Accounts receivable, net	6,459,000	$ 4,155,000	$ 6,459,000
Sales Revenue, Net | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Number of customers | Customer		1	1	1
Concentration risk, percentage		10.00%	10.00%	12.40%
Net Accounts Receivable | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Number of customers | Customer		2	2
Concentration risk, percentage		10.00%	10.00%
Sales Revenue, Services, Net | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk, percentage				72.60%
Raw materials | Supplier Concentration Risk | Vendor one
Significant Accounting Policies [Line Items]
Concentration risk, percentage		20.00%	19.70%
Raw materials | Supplier Concentration Risk | Vendor two
Significant Accounting Policies [Line Items]
Concentration risk, percentage		11.90%	15.40%
Raw materials | Supplier Concentration Risk | Vendor three
Significant Accounting Policies [Line Items]
Concentration risk, percentage		10.20%	9.50%
Forward Contracts
Significant Accounting Policies [Line Items]
Payable		$ 472,000
Accounts receivable, net	$ 66,000		$ 66,000
Lifetime Warranties | Direct-to-Consumer
Significant Accounting Policies [Line Items]
Sales revenue		$ 14,874,000	$ 10,820,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Sales Revenue Disaggregated by Sales Channel and Geographic Region (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation Of Revenue [Line Items]
Total sales revenue	$ 336,015	$ 225,492	$ 168,170
Business to Business | Domestic
Disaggregation Of Revenue [Line Items]
Total sales revenue	116,581	83,390	56,605
Business to Business | International
Disaggregation Of Revenue [Line Items]
Total sales revenue	77,333	55,519	50,106
Direct-to-Consumer | Domestic
Disaggregation Of Revenue [Line Items]
Total sales revenue	$ 142,101	$ 86,583	$ 61,459

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Summary of Fair Value Assets Measured on Recurring Basis for Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 196,634	$ 142,953
Fair Value Measurements Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Adjusted cost	240,358	173,970
Gross unrealized gains (losses)	(9)	(26)
Fair value	240,349	173,944
Cash and cash equivalents	196,634	142,953
Marketable securities	43,715	30,991
Fair Value Measurements Recurring | Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Adjusted cost	33,671	46,237
Fair value	33,671	46,237
Cash and cash equivalents	33,671	46,237
Fair Value Measurements Recurring | Level 1 | Money Market Accounts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Adjusted cost	158,438	93,430
Fair value	158,438	93,430
Cash and cash equivalents	158,438	93,430
Fair Value Measurements Recurring | Level 2 | Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Adjusted cost	13,629	20,789
Gross unrealized gains (losses)	(16)	(21)
Fair value	13,613	20,768
Cash and cash equivalents		2,796
Marketable securities	13,613	17,972
Fair Value Measurements Recurring | Level 2 | U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Adjusted cost	34,620	499
Gross unrealized gains (losses)	7
Fair value	34,627	499
Cash and cash equivalents	4,525
Marketable securities	$ 30,102	499
Fair Value Measurements Recurring | Level 2 | Certificates Of Deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Adjusted cost		11,010
Gross unrealized gains (losses)		(4)
Fair value		11,006
Cash and cash equivalents		490
Marketable securities		10,516
Fair Value Measurements Recurring | Level 2 | Agency Mortgage-backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Adjusted cost		2,005
Gross unrealized gains (losses)		(1)
Fair value		2,004
Marketable securities		$ 2,004

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Summary of Estimated Fair Value of Company's Investments in Marketable Securities Classified by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Available For Sale Securities [Abstract]
Due within one year	$ 43,715
Total	$ 43,715	$ 30,991

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Summary of Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 272	$ (35)
Other comprehensive gain (loss)	452	307	$ 2
Ending Balance	724	272	(35)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	363
Other comprehensive gain (loss)	31	363
Ending Balance	394	363
Unrealized Gain (Losses) on Marketable Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(17)	(82)
Other comprehensive gain (loss)	17	65
Ending Balance		(17)	(82)
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(74)	47
Other comprehensive gain (loss)	404	(121)
Ending Balance	$ 330	$ (74)	$ 47

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Summary of Cash, Cash Equivalents and Short-term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Cash and cash equivalents
Cash	$ 33,671	$ 46,237
Money market accounts	158,438	93,430
Certificates of deposit		490
Corporate bonds		2,796
U.S. Treasury securities	4,525
Total cash and cash equivalents	196,634	142,953
Marketable securities
Marketable securities	43,715	30,991
Certificates Of Deposit
Marketable securities
Marketable securities		10,516
Corporate Bonds
Marketable securities
Marketable securities	13,613	17,972
Agency Mortgage-backed Securities
Marketable securities
Marketable securities		2,004
U.S. Treasury Securities
Marketable securities
Marketable securities	$ 30,102	$ 499

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Schedule of Gross Accounts Receivable Balance Concentrations by Major Category (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accounts Notes And Loans Receivable [Line Items]
Gross accounts receivable	$ 39,062	$ 34,710
Gross accounts receivable, percentage	100.00%	100.00%
Rental
Accounts Notes And Loans Receivable [Line Items]
Gross accounts receivable	$ 3,406	$ 6,236
Gross accounts receivable, percentage	8.70%	18.00%
Business To Business And Other Receivables
Accounts Notes And Loans Receivable [Line Items]
Gross accounts receivable	$ 35,656	$ 28,474
Gross accounts receivable, percentage	91.30%	82.00%

Summary of Significant Accou_11

Summary of Significant Accounting Policies - Schedule of Net Accounts Receivable Balance Concentrations by Major Category (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accounts Notes And Loans Receivable [Line Items]
Net accounts receivable	$ 37,041	$ 31,444
Net accounts receivable, percentage	100.00%	100.00%
Rental
Accounts Notes And Loans Receivable [Line Items]
Net accounts receivable	$ 2,413	$ 4,212
Net accounts receivable, percentage	6.50%	13.40%
Business To Business And Other Receivables
Accounts Notes And Loans Receivable [Line Items]
Net accounts receivable	$ 34,628	$ 27,232
Net accounts receivable, percentage	93.50%	86.60%

Summary of Significant Accou_12

Summary of Significant Accounting Policies - Schedule of Net Accounts Receivable Balance Concentrations by Major Category (Parenthetical) (Details)	12 Months Ended
	Dec. 31, 2018USD ($)Customer	Dec. 31, 2017USD ($)Customer
Accounts Notes And Loans Receivable [Line Items]
Gross accounts receivable	$ 39,062,000	$ 34,710,000
Customer Concentration Risk | Business To Business Receivables
Accounts Notes And Loans Receivable [Line Items]
Number of customers | Customer	1	1
Gross accounts receivable	$ 16,198,000	$ 10,394,000
Credit insurance policy, deductible amount	$ 400,000
Credit insurance policy, retention percentage	10.00%
Customer Concentration Risk | Business To Business Receivables | Maximum
Accounts Notes And Loans Receivable [Line Items]
Credit insurance policy, coverage limit	$ 18,000,000	$ 12,000,000

Summary of Significant Accou_13

Summary of Significant Accounting Policies - Schedule of Net Accounts Receivable Balance by Aging Category by Invoice Due Date (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accounts Notes And Loans Receivable [Line Items]
Accounts receivable, net	$ 37,041	$ 31,444
Net accounts receivable, percentage	100.00%	100.00%
Held And Unbilled
Accounts Notes And Loans Receivable [Line Items]
Accounts receivable, net	$ 80	$ 537
Net accounts receivable, percentage	0.20%	1.70%
Aged 0-90 Days
Accounts Notes And Loans Receivable [Line Items]
Accounts receivable, net	$ 36,245	$ 29,237
Net accounts receivable, percentage	97.90%	93.00%
Aged 91-180 Days
Accounts Notes And Loans Receivable [Line Items]
Accounts receivable, net	$ 425	$ 435
Net accounts receivable, percentage	1.10%	1.40%
Aged 181-365 Days
Accounts Notes And Loans Receivable [Line Items]
Accounts receivable, net	$ 234	$ 602
Net accounts receivable, percentage	0.60%	1.90%
Aged Over 365 Days
Accounts Notes And Loans Receivable [Line Items]
Accounts receivable, net	$ 57	$ 633
Net accounts receivable, percentage	0.20%	2.00%

Summary of Significant Accou_14

Summary of Significant Accounting Policies - Schedule of Allowances for Accounts Receivable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Allowances - accounts receivable
Doubtful accounts	$ 693	$ 1,415
Rental revenue adjustments	438	947
Sales returns	890	904
Total allowances - accounts receivable	$ 2,021	$ 3,266
Doubtful accounts, percentage	1.80%	4.10%
Rental revenue adjustments, percentage	1.10%	2.70%
Sales returns, percentage	2.30%	2.60%
Total allowances - accounts receivable, percentage	5.20%	9.40%

Summary of Significant Accou_15

Summary of Significant Accounting Policies - Breakdown of the Company Revenue (Details) - USD ($) $ 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
Concentration Risk [Line Items]
Revenues	$ 86,531	$ 95,291	$ 97,238	$ 79,051	$ 63,787	$ 69,030	$ 64,121	$ 52,500	$ 358,111	$ 249,438	$ 202,829
U.S. revenue
Concentration Risk [Line Items]
Revenues									280,778	193,919	152,723
Non-U.S. revenue
Concentration Risk [Line Items]
Revenues									$ 77,333	$ 55,519	$ 50,106

Summary of Significant Accou_16

Summary of Significant Accounting Policies - Schedule of Inventories (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials and work-in-progress	$ 24,980	$ 16,324
Finished goods	2,756	2,917
Less: reserves	(665)	(399)
Inventories	$ 27,071	$ 18,842

Summary of Significant Accou_17

Summary of Significant Accounting Policies - Computation of Depreciation and Amortization Using Straight Line Method Over Estimated Useful Lives of Assets (Details)	12 Months Ended
	Dec. 31, 2018
Rental equipment | Minimum
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	1 year 6 months
Rental equipment | Maximum
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	5 years
Manufacturing equipment and tooling | Minimum
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	3 years
Manufacturing equipment and tooling | Maximum
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	5 years
Computer equipment and software | Minimum
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	2 years
Computer equipment and software | Maximum
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	3 years
Furniture and equipment | Minimum
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	3 years
Furniture and equipment | Maximum
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	5 years
Leasehold improvements
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	Lesser of estimated useful life or remaining lease term

Summary of Significant Accou_18

Summary of Significant Accounting Policies - Summary of Depreciation and Amortization Expense of Rental Equipment and Other Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Depreciation	$ 7,567	$ 9,835	$ 11,429
Depreciation and amortization	10,030	11,795	13,457
Equipment
Property Plant And Equipment [Line Items]
Depreciation	7,567	9,835	11,429
Other property and equipment
Property Plant And Equipment [Line Items]
Depreciation and amortization	$ 2,463	$ 1,960	$ 2,028

Summary of Significant Accou_19

Summary of Significant Accounting Policies - Summary of Property Plant and Equipment and Rental Equipment with Associated Accumulated Depreciation (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment	$ 64,634	$ 64,568
Accumulated depreciation	42,293	44,465
Property and equipment, net	22,341	20,103
Equipment
Property Plant And Equipment [Line Items]
Property and equipment	43,038	49,349
Accumulated depreciation	31,813	34,754
Property and equipment, net	11,225	14,595
Other property and equipment
Property Plant And Equipment [Line Items]
Property and equipment	21,596	15,219
Accumulated depreciation	10,480	9,711
Property and equipment, net	$ 11,116	$ 5,508

Summary of Significant Accou_20

Summary of Significant Accounting Policies - Summary of Property Plant and Equipment and Rental Equipment with Associated Accumulated Depreciation (Parenthetical) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Rental equipment, allowance	$ 594	$ 754

Summary of Significant Accou_21

Summary of Significant Accounting Policies - Computation of Earnings Per Share (Details) - 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
Numerator—basic and diluted:
Net income	$ 10,045	$ 16,432	$ 14,610	$ 10,758	$ (606)	$ 7,338	$ 8,338	$ 5,932	$ 51,845	$ 21,002	$ 20,519
Denominator:
Weighted-average common shares - basic common stock	21,544,202	21,324,256	21,172,170	21,026,154	20,869,589	20,753,789	20,622,320	20,489,532	21,266,696	20,683,807	20,067,152
Weighted-average common shares - diluted common stock	22,600,038	22,659,052	22,503,749	22,295,213	22,167,358	21,998,660	21,848,359	21,579,721	22,514,513	21,897,988	21,095,867
Net income per share - basic common stock	$ 0.47	$ 0.77	$ 0.69	$ 0.51	$ (0.03)	$ 0.35	$ 0.40	$ 0.29	$ 2.44	$ 1.02	$ 1.02
Net income per share - diluted common stock	$ 0.44	$ 0.73	$ 0.65	$ 0.48	$ (0.03)	$ 0.33	$ 0.38	$ 0.27	$ 2.30	$ 0.96	$ 0.97
Denominator calculation from basic to diluted:
Weighted-average common shares - basic common stock	21,544,202	21,324,256	21,172,170	21,026,154	20,869,589	20,753,789	20,622,320	20,489,532	21,266,696	20,683,807	20,067,152
Stock options and other dilutive awards									1,247,817	1,214,181	1,028,715
Weighted-average common shares - diluted common stock	22,600,038	22,659,052	22,503,749	22,295,213	22,167,358	21,998,660	21,848,359	21,579,721	22,514,513	21,897,988	21,095,867
Shares excluded from diluted weighted-average shares:
Shares excluded from diluted weighted-average shares									39,330	63,313	841,760
Stock options
Shares excluded from diluted weighted-average shares:
Shares excluded from diluted weighted-average shares										37,249	841,760
Restricted stock units and restricted stock awards
Shares excluded from diluted weighted-average shares:
Shares excluded from diluted weighted-average shares									39,330	26,064

Goodwill and Other Identifiab_3

Goodwill and Other Identifiable Intangible Assets - Schedule of Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Beginning Balance	$ 2,363
Acquisition		$ 2,154
Translation adjustment	(106)	209
Ending Balance	$ 2,257	$ 2,363

Goodwill and Other Identifiab_4

Goodwill and Other Identifiable Intangible Assets - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill And Intangible Assets Disclosure [Abstract]
Impairment of finite lived intangible assets	$ 0	$ 0
Amortization of intangible assets	$ 1,265,000	$ 507,000	$ 101,000

Goodwill and Other Identifiab_5

Goodwill and Other Identifiable Intangible Assets - Summary of Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	$ 6,584	$ 6,338
Accumulated amortization	2,829	1,621
Net amount	$ 3,755	$ 4,717
Licenses
Finite Lived Intangible Assets [Line Items]
Average estimated useful lives (in years)	10 years	10 years
Gross carrying amount	$ 185	$ 185
Accumulated amortization	155	137
Net amount	$ 30	$ 48
Patents And Websites
Finite Lived Intangible Assets [Line Items]
Average estimated useful lives (in years)	5 years	5 years
Gross carrying amount	$ 4,164	$ 4,173
Accumulated amortization	1,640	959
Net amount	$ 2,524	$ 3,214
Customer Relationships
Finite Lived Intangible Assets [Line Items]
Average estimated useful lives (in years)	4 years	4 years
Gross carrying amount	$ 1,373	$ 1,437
Accumulated amortization	572	240
Net amount	$ 801	$ 1,197
Non-Compete Agreement
Finite Lived Intangible Assets [Line Items]
Average estimated useful lives (in years)	2 years 3 months 18 days	3 years
Gross carrying amount	$ 229	$ 240
Accumulated amortization	154	52
Net amount	75	188
Commercials
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	633	303
Accumulated amortization	308	233
Net amount	$ 325	$ 70
Commercials | Minimum
Finite Lived Intangible Assets [Line Items]
Average estimated useful lives (in years)	2 years	2 years
Commercials | Maximum
Finite Lived Intangible Assets [Line Items]
Average estimated useful lives (in years)	3 years	3 years

Goodwill and Other Identifiab_6

Goodwill and Other Identifiable Intangible Assets - Schedule of Annual Estimated Amortization Expense (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
2,019	$ 1,234
2,020	1,132
2,021	844
2,022	545
Net amount	$ 3,755	$ 4,717

Current Liabilities - Schedule

Current Liabilities - Schedule of Accounts Payable and Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accounts payable	$ 13,720	$ 9,541
Accrued inventory (in-transit and unvouchered receipts) and trade payables	9,597	7,252
Accrued purchasing card liability	2,089	2,381
Accrued franchise, sales and use taxes	518	479
Other accrued expenses	862	973
Accounts payable and accrued expenses	$ 26,786	$ 20,626

Current Liabilities - Schedul_2

Current Liabilities - Schedule of Accrued Payroll (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued bonuses	$ 4,780	$ 3,086
Accrued wages and other payroll related items	3,494	1,746
Accrued vacation	1,959	1,338
Accrued employee stock purchase plan deductions	1,174	707
Accrued payroll	$ 11,407	$ 6,877

Income Taxes - Components of In

Income Taxes - Components of Income Before Provision for Income Taxes (Details) - USD ($) $ 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
Income Tax Disclosure [Abstract]
United States									$ 40,245	$ 29,121	$ 22,725
Foreign									210	535
Income before provision (benefit) for income taxes	$ 5,823	$ 11,299	$ 13,646	$ 9,687	$ 5,794	$ 8,817	$ 9,166	$ 5,879	$ 40,455	$ 29,656	$ 22,725

Income Taxes - Components of Pr

Income Taxes - Components of Provision for Income Taxes (Details) - USD ($) $ 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
Current tax expense (benefit)
Federal										$ 245	$ 451
State									$ (40)	240	776
Foreign									171	206
Total current tax expense									131	691	1,227
Deferred tax expense (benefit)
Federal									(9,774)	8,709	1,357
State									(1,630)	92	590
Foreign									(117)	(71)
Total deferred tax expense (benefit)									(11,521)	8,730	1,947
Tax benefit for change in valuation allowance										(767)	(968)
Total deferred tax expense (benefit), net									(11,521)	7,963	979
Income tax expense (benefit)	$ (4,222)	$ (5,133)	$ (964)	$ (1,071)	$ 6,400	$ 1,479	$ 828	$ (53)	$ (11,390)	$ 8,654	$ 2,206

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets (liabilities)
Accrued expenses	$ 8,033	$ 5,669
Net operating loss and credit carryforward	19,805	10,378
Allowance, reserves and other	3,490	3,301
Stock-based compensation	3,253	2,598
Deferred tax assets	34,581	21,946
Property, plant, and equipment	(4,683)	(3,658)
Total	$ 29,898	$ 18,288

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of the Federal Statutory Income Tax Rate to the Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
U.S. Statutory rate	21.00%	34.00%	34.00%
State income taxes, net of federal benefit	(3.73%)	0.37%	0.88%
Stock-based compensation	(45.01%)	(30.40%)	(23.74%)
Change in valuation allowance		(2.59%)	(4.26%)
R&D credit, net of reserve	(1.39%)	(1.43%)	(1.75%)
Expiration of net operating losses		2.76%	4.51%
Effect of U.S tax law change		25.55%
Other	0.98%	0.92%	0.07%
Effective income tax rate	(28.15%)	29.18%	9.71%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Corporate tax rate		21.00%	34.00%	34.00%
Provisional net charge related to TCJA	$ 7,578,000
Tax expense (benefit) for change in valuation allowance			$ 767,000	$ 968,000
Unrecognized tax benefits, interest or penalties recognized		$ 0	0	0
Unrecognized tax benefits that, if recognized, would affect the effective tax rate	1,062,000	1,294,000	1,062,000	$ 934,000
California
Income Tax Contingency [Line Items]
Research and development credits carryforwards		2,800,000
Valuation allowance	$ 0	0	0
Tax expense (benefit) for change in valuation allowance			$ 767,000
Federal
Income Tax Contingency [Line Items]
Net operating loss carryforwards		$ 67,088,000
Net operating loss carryforwards expiration, beginning year		2,026
Research and development credits carryforwards		$ 2,743,000
Research and development credits carryforwards expiration, beginning year		2,022
State
Income Tax Contingency [Line Items]
Net operating loss carryforwards		$ 27,661,000
Net operating loss carryforwards expiration, beginning year		2,028

Income Taxes - Summary of Recon

Income Taxes - Summary of Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of liability for unrecognized tax benefits
Balance at beginning of period	$ 1,062	$ 934	$ 773
Additions based on tax positions related to current year	232	128	161
Balance at end of period	$ 1,294	$ 1,062	$ 934

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018USD ($)Voteshares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)shares
Class Of Stock [Line Items]
Number of voting rights per share of common stock | Vote	1
Preferred stock, shares authorized	10,000,000
Preferred stock, shares issued		0
Preferred stock, shares outstanding		0
Dividends declared | $	$ 0	$ 0	$ 0
Total intrinsic value of options exercised | $	98,743,000	33,931,000	22,228,000
Stock-based compensation, unrecognized expense, nonvested granted awards | $	4,072,000
Total weighted average fair value of stock options granted | $	0	8,929,000	6,408,000
401(k) Retirement Savings Plan
Class Of Stock [Line Items]
Defined benefit plan, contributed by employer net of forfeitures | $	$ 865,000	$ 557,000	$ 0
Stock options
Class Of Stock [Line Items]
Rate of reduced stock-based compensation expense for estimated forfeiture	7.30%	7.30%	6.90%
Time based restricted stock units
Class Of Stock [Line Items]
Vesting period	4 years
Grants of units unvested	31,877	42,028
Time based restricted stock awards
Class Of Stock [Line Items]
Vesting period	4 years
Grants of units unvested	22,645	20,789
Performance and time based restricted stock awards
Class Of Stock [Line Items]
Vesting period	3 years
Grants of units unvested	33,964	20,785
Performance and time based restricted stock units
Class Of Stock [Line Items]
Vesting period	3 years
Grants of units unvested		13,109
Restricted stock units and restricted stock awards
Class Of Stock [Line Items]
Unrecognized compensation cost related to unvested employee excluding estimated forfeitures | $	$ 10,091,000
Amount expected to recognized over weighted-average period	2 years 8 months 12 days
Rate of reduced stock-based compensation expense for estimated forfeiture	4.70%	6.00%
Grants of units unvested			0
Maximum | Stock options
Class Of Stock [Line Items]
Stock option period, expiration	10 years
Vesting period	4 years
Minimum | Stock options
Class Of Stock [Line Items]
Stock option period, expiration	7 years
Vesting period	1 year
2002 Plan
Class Of Stock [Line Items]
Stock option shares outstanding	4,123
Number of equity awards available for grant	0
2012 Plan
Class Of Stock [Line Items]
Stock option shares outstanding	168,016
Number of equity awards available for grant	0
2014 Plan
Class Of Stock [Line Items]
Stock option shares outstanding	1,095,964
Number of equity awards available for grant	1,910,864
Terms of shares available for issuance	The number of shares available for issuance under the 2014 Plan also is increased annually on the first day of each fiscal year equal to the least of: 895,346 shares; 4% of the outstanding shares of common stock as of the last day of the Company's immediately preceding fiscal year; or such other amount as the Company's board of directors may determine.
Common stock capital shares reserved for future issuance maximum annual increase	895,346
Percentage on outstanding shares of common stock	4.00%
Number of additional number of shares reserve to provision	839,054
2012 Plan and 2002 Plan | Maximum
Class Of Stock [Line Items]
Stock option shares outstanding	2,328,569
2014 ESPP Plan
Class Of Stock [Line Items]
Number of equity awards available for grant	746,448
Terms of shares available for issuance	The number of shares available for sale under the ESPP is increased annually on the first day of each fiscal year equal to the least of: 179,069 shares; 1.5% of the outstanding shares of the Company?s common stock on the last day of the Company?s immediately preceding fiscal year; or such other amount as may be determined by the administrator.
Percentage on outstanding shares of common stock	1.50%
Number of additional number of shares reserve to provision	179,069
Maximum percentage of common stock eligible to purchase through payroll deductions for participants	15.00%
Maximum number of shares available for participant to purchase during period	1,500
Purchase price as percentage of stock price on offering period	85.00%
Purchase price as percentage of stock price on exercise date	85.00%
Potential increase of shares available for issuance	179,069

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Stock Options Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class Of Stock [Line Items]
Stock Options Outstanding, Beginning balance	1,836,426	2,355,527	2,295,370
Stock Options, Granted		64,498	683,998
Stock Options, Exercised	(708,319)	(520,393)	(570,079)
Stock Options, Forfeited	(771)	(63,173)	(53,247)
Stock Options, Expired		(33)	(515)
Stock Options Outstanding, Ending balance	1,127,336	1,836,426	2,355,527	2,295,370
Stock Options, Vested and exercisable	851,039	1,176,504	1,023,865
Stock Options, Vested and expected to vest	1,109,280	1,792,871	2,259,811
Price per share, Granted		$ 83.30
Price per share, Expired		8.70	$ 8.70
Outstanding, Weighted-average exercise price, Beginning balance	$ 30.77	28.22	19.36
Weighted-average exercise price, Granted		83.30	44.70
Weighted-average exercise price, Exercised	24.22	24.16	12.32
Weighted-average exercise price, Forfeited	28.24	43.74	28.09
Weighted-average exercise price, Expired		8.70	8.70
Outstanding, Weighted-average exercise price, Ending balance	34.89	30.77	28.22	$ 19.36
Weighted-average exercise price, Vested and exercisable	32.12	24.33	16.61
Weighted-average exercise price, Vested and expected to vest	$ 34.75	$ 30.50	$ 27.95
Remaining weighted-average contractual term, Outstanding	3 years 10 months 2 days	4 years 6 months 29 days	5 years 5 months 1 day	5 years 11 months 23 days
Remaining weighted-average contractual term, Vested and exercisable	3 years 9 months	4 years 4 months 20 days	4 years 11 months 15 days
Remaining weighted-average contractual term, Vested and expected to vest	3 years 10 months 2 days	4 years 6 months 29 days	5 years 4 months 24 days
Outstanding, Per share average intrinsic value	$ 89.28	$ 88.31	$ 38.95	$ 21.07
Per share average intrinsic value, Vested and exercisable	92.05	94.75	50.56
Per share average intrinsic value, Vested and expected to vest	89.42	88.58	39.22
Minimum
Class Of Stock [Line Items]
Outstanding, Price per share, Beginning balance	0.60	0.60	0.60
Price per share, Granted			37.10
Price per share, Exercised	0.60	0.60	0.60
Price per share, Forfeited	24.52	24.52	0.75
Outstanding, Price per share, Ending balance	0.75	0.60	0.60	0.60
Price per share, Vested and exercisable	0.75	0.60	0.60
Price per share, Vested and expected to vest	0.75	0.60	0.60
Maximum
Class Of Stock [Line Items]
Outstanding, Price per share, Beginning balance	83.30	58.95	46.66
Price per share, Granted			58.95
Price per share, Exercised	58.95	58.95	46.66
Price per share, Forfeited	44.19	58.95	44.19
Outstanding, Price per share, Ending balance	83.30	83.30	58.95	$ 46.66
Price per share, Vested and exercisable	83.30	83.30	46.66
Price per share, Vested and expected to vest	$ 83.30	$ 83.30	$ 46.66

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of Restricted Stock Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Time based restricted stock units
Class Of Stock [Line Items]
Unvested restricted stock units/ awards outstanding, Beginning balance	42,028
Granted	31,877	42,028
Vested	(13,742)
Forfeited/canceled	(1,574)
Unvested restricted stock units/ awards outstanding, Ending balance	58,589	42,028
Performance and time based restricted stock units
Class Of Stock [Line Items]
Unvested restricted stock units/ awards outstanding, Beginning balance	13,109
Granted		13,109
Vested	(4,370)
Unvested restricted stock units/ awards outstanding, Ending balance	8,739	13,109
Restricted stock units
Class Of Stock [Line Items]
Unvested restricted stock units/ awards outstanding, Beginning balance	55,137
Granted	31,877	55,137
Vested	(18,112)
Forfeited/canceled	(1,574)
Unvested restricted stock units/ awards outstanding, Ending balance	67,328	55,137
Unvested and expected to vest restricted stock units/awards outstanding	62,504	48,589
Weighted-average grant date fair value per share, Unvested restricted stock units/ awards outstanding, Beginning balance	$ 90.05
Weighted-average grant date fair value per share, Granted	143.50	$ 90.05
Weighted-average grant date fair value per share, Vested	89.35
Weighted-average grant date fair value per share, Forfeited/canceled	106.55
Weighted-average grant date fair value per share, Unvested restricted stock units/ awards outstanding, Ending balance	115.16	90.05
Weighted-average grant date fair value per share, Unvested and expected to vest restricted stock units/awards outstanding	$ 115.98	$ 89.95
Time based restricted stock awards
Class Of Stock [Line Items]
Unvested restricted stock units/ awards outstanding, Beginning balance	20,789
Granted	22,645	20,789
Vested	(6,497)
Unvested restricted stock units/ awards outstanding, Ending balance	36,937	20,789
Performance and time based restricted stock awards
Class Of Stock [Line Items]
Unvested restricted stock units/ awards outstanding, Beginning balance	20,785
Granted	33,964	20,785
Vested	(6,928)
Unvested restricted stock units/ awards outstanding, Ending balance	47,821	20,785
Restricted stock awards
Class Of Stock [Line Items]
Unvested restricted stock units/ awards outstanding, Beginning balance	41,574
Granted	56,609	41,574
Vested	(13,425)
Unvested restricted stock units/ awards outstanding, Ending balance	84,758	41,574
Unvested and expected to vest restricted stock units/awards outstanding	65,773	34,051
Weighted-average grant date fair value per share, Unvested restricted stock units/ awards outstanding, Beginning balance	$ 91.52
Weighted-average grant date fair value per share, Granted	130.89	$ 91.52
Weighted-average grant date fair value per share, Vested	91.52
Weighted-average grant date fair value per share, Unvested restricted stock units/ awards outstanding, Ending balance	115.80	91.52
Weighted-average grant date fair value per share, Unvested and expected to vest restricted stock units/awards outstanding	$ 115.85	$ 91.52

Stockholders' Equity - Summar_3

Stockholders' Equity - Summary of Stock-based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-based compensation expense by type of award:
Stock-based compensation expense	$ 12,790	$ 9,640	$ 7,294
Stock Option Plan Awards
Stock-based compensation expense by type of award:
Stock-based compensation expense	6,015	7,652	6,850
Restricted stock units and restricted stock awards
Stock-based compensation expense by type of award:
Stock-based compensation expense	5,890	1,447
Employee Stock Purchase Plan
Stock-based compensation expense by type of award:
Stock-based compensation expense	$ 885	$ 541	$ 444

Stockholders' Equity - Summar_4

Stockholders' Equity - Summary of Stock-based Compensation Expense Recognized in Income Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class Of Stock [Line Items]
Stock-based compensation expense	$ 12,790	$ 9,640	$ 7,294
Cost of Revenue
Class Of Stock [Line Items]
Stock-based compensation expense	1,060	845	639
Research and Development
Class Of Stock [Line Items]
Stock-based compensation expense	1,314	1,015	776
Sales and Marketing
Class Of Stock [Line Items]
Stock-based compensation expense	2,355	1,558	1,142
General and Administrative
Class Of Stock [Line Items]
Stock-based compensation expense	$ 8,061	$ 6,222	$ 4,737

Stockholders' Equity - Assumpti

Stockholders' Equity - Assumptions Applied to Estimate Fair Value of Stock Option Awards (Details) - Stock options	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk free interest rate, Minimum	1.65%	1.00%
Risk free interest rate, Maximum	1.73%	1.40%
Expected dividend yield	0.00%	0.00%
Volatility, Minimum	41.61%	43.95%
Volatility, Maximum	42.15%	45.93%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	3 years 6 months 14 days	3 years 6 months 14 days
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	4 years	5 years 5 months 23 days

Stockholders' Equity - Assump_2

Stockholders' Equity - Assumptions Applied to Estimate Fair Value of Shares Issued Under ESPP (Details) - Employee Stock Purchase Plan	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 months	6 months	6 months
Risk free interest rate, Minimum	1.63%	1.15%	1.15%
Risk free interest rate, Maximum	2.46%	1.63%	1.32%
Expected dividend yield	0.00%	0.00%	0.00%
Volatility, Minimum	37.34%	42.35%	43.28%
Volatility, Maximum	44.00%	45.34%	44.81%

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments And Contingencies [Line Items]
Rent expense	$ 1,638	$ 1,148	$ 1,028
Outstanding purchase orders with its outside vendors and suppliers	61,000
MedSupport Systems B.V.
Commitments And Contingencies [Line Items]
Rent expense	$ 33	$ 21
Offices and Certain Equipment
Commitments And Contingencies [Line Items]
Operating leases expiration date	Sep. 30, 2024

Commitments and Contingencies_2

Commitments and Contingencies - Minimum Aggregate Payments Due under Operating Leases and Specified Non-Cancelable Contractual Obligations Consist of Software License and Maintenance Agreements (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments And Contingencies Disclosure [Abstract]
Operating leases, 2019	$ 2,450
Operating leases, 2020	2,212
Operating leases, 2021	1,593
Operating leases, 2022	1,273
Operating leases, 2023	1,215
Operating leases, Thereafter	917
Operating leases, Total minimum payments	9,660
Related party leases, 2019	31
Related party leases, 2020	10
Related party leases, Total minimum payments	41
Non-cancelable contractual obligations, 2018	578
Non-cancelable contractual obligations, 2019	578
Non-cancelable contractual obligations, 2020	457
Non-cancelable contractual obligations, Total minimum payments	1,613
2,019	3,059
2,020	2,800
2,021	2,050
2,022	1,273
2,023	1,215
Thereafter	917
Total minimum payments	$ 11,314

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Changes in Aggregate Product Warranty Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Product warranty liability at beginning of period	$ 6,171	$ 3,480	$ 1,973
Accruals for warranties issued	7,693	5,275	3,123
Adjustments related to preexisting warranties (including changes in estimates)	90	200	118
Settlements made (in cash or in kind)	(4,424)	(2,784)	(1,734)
Product warranty liability at end of period	$ 9,530	$ 6,171	$ 3,480

Foreign Currency Exchange Con_2

Foreign Currency Exchange Contracts and Hedging - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018USD ($)Contract	Dec. 31, 2017USD ($)Contract	Dec. 31, 2016USD ($)
Derivatives Fair Value [Line Items]
Number of contract designated hedges | Contract	29	18
Number of contract non-designated hedges | Contract	4	3
Non-Designated Derivative Contracts
Derivatives Fair Value [Line Items]
Derivative contracts notional amounts	$ 2,336,000	$ 2,350,000
Designated Derivative Contracts
Derivatives Fair Value [Line Items]
Derivative contracts notional amounts	21,374,000	13,818,000
Unrealized (loss) gain on derivative	$ 404,000	$ (121,000)	$ 47,000
Minimum
Derivatives Fair Value [Line Items]
Derivative contracts expiration period	1 month
Maximum
Derivatives Fair Value [Line Items]
Derivative contracts expiration period	12 months

Quarterly Summary of Informat_3

Quarterly Summary of Information (Unaudited) - Summary of Unaudited Quarterly Statements of Income Data (Details) - 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
Selected Quarterly Financial Information [Abstract]
Total revenue	$ 86,531	$ 95,291	$ 97,238	$ 79,051	$ 63,787	$ 69,030	$ 64,121	$ 52,500	$ 358,111	$ 249,438	$ 202,829
Gross profit	43,570	48,813	48,470	37,727	30,756	33,170	31,567	25,744	178,580	121,237	97,310
Income before provision (benefit) for income taxes	5,823	11,299	13,646	9,687	5,794	8,817	9,166	5,879	40,455	29,656	22,725
Provision (benefit) for income taxes	(4,222)	(5,133)	(964)	(1,071)	6,400	1,479	828	(53)	(11,390)	8,654	2,206
Net income	$ 10,045	$ 16,432	$ 14,610	$ 10,758	$ (606)	$ 7,338	$ 8,338	$ 5,932	$ 51,845	$ 21,002	$ 20,519
Net income (loss) per share attributable to common stockholders
Net income (loss) per share - basic common stock	$ 0.47	$ 0.77	$ 0.69	$ 0.51	$ (0.03)	$ 0.35	$ 0.40	$ 0.29	$ 2.44	$ 1.02	$ 1.02
Net income (loss) per share - diluted common stock	$ 0.44	$ 0.73	$ 0.65	$ 0.48	$ (0.03)	$ 0.33	$ 0.38	$ 0.27	$ 2.30	$ 0.96	$ 0.97
Weighted-average number of shares used in calculating net income per share attributable to common stockholders:
Basic common shares	21,544,202	21,324,256	21,172,170	21,026,154	20,869,589	20,753,789	20,622,320	20,489,532	21,266,696	20,683,807	20,067,152
Diluted common shares	22,600,038	22,659,052	22,503,749	22,295,213	22,167,358	21,998,660	21,848,359	21,579,721	22,514,513	21,897,988	21,095,867

Schedule II_ Valuation and Qu_2

Schedule II: Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 1,415	$ 1,869	$ 1,664
Additions	1,685	3,864	3,580
Deletions	2,677	4,418	2,575
Adjustments	270	100	(800)
Balance at End of Year	693	1,415	1,869
Allowance for Sales Returns
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	904	585	366
Additions	15,834	9,909	7,502
Deletions	15,848	9,590	7,283
Balance at End of Year	890	904	585
Allowance for Rental Revenue Adjustments
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	947	6,078	4,115
Additions	2,678	5,057	10,777
Deletions	2,917	10,088	9,614
Adjustments	(270)	(100)	800
Balance at End of Year	438	947	6,078
Allowance for Rental Asset Loss
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	754	725	850
Additions	408	561	455
Deletions	568	532	580
Balance at End of Year	$ 594	$ 754	$ 725