Etsy (ETSY) 10-K 1 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 23, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	ETSY INC
Entity Central Index Key	1,370,637
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		121,502,754
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 1,748,789,745

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 315,442	$ 181,592
Short-term investments	25,108	100,494
Accounts receivable, net	33,677	26,426
Prepaid and other current assets	20,379	15,571
Deferred tax charge—current	0	17,132
Funds receivable and seller accounts	44,658	29,817
Total current assets	439,264	371,032
Restricted cash	5,341	5,341
Property and equipment, net	117,617	126,407
Goodwill	38,541	35,657
Intangible assets, net	4,100	7,507
Deferred tax charge—net of current portion	0	34,264
Other assets	720	985
Total assets	605,583	581,193
Current liabilities:
Accounts payable	13,622	10,978
Accrued expenses	28,743	24,179
Capital lease obligations—current	5,798	6,829
Funds payable and amounts due to sellers	44,658	29,817
Deferred revenue	6,262	5,648
Other current liabilities	3,394	6,557
Total current liabilities	102,477	84,008
Capital lease obligations—net of current portion	4,115	5,296
Deferred tax liabilities	23,786	65,068
Facility financing obligation	60,049	57,360
Other liabilities	18,262	24,704
Total liabilities	208,689	236,436
Commitments and Contingencies
Stockholders’ equity:
Common stock ($0.001 par value, 120,000,000 and 1,400,000,000 shares authorized as of December 31, 2014 and December 31, 2015; 44,180,939 and 112,563,354 shares issued and outstanding as of December 31, 2014, and December 31, 2015, respectively)	122	116
Preferred stock ($0.001 par value, 25,000,000 shares authorized as of December 31, 2017 and 2016)	0	0
Additional paid-in capital	499,441	442,510
Accumulated deficit	(96,290)	(116,341)
Accumulated other comprehensive (loss) income	(6,379)	18,472
Total stockholders’ equity	396,894	344,757
Total liabilities, convertible preferred stock and stockholders’ equity	$ 605,583	$ 581,193

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	1,400,000,000	1,400,000,000
Common stock, shares issued (in shares)	121,769,238	115,973,039
Common stock, shares outstanding (in shares)	121,769,238	115,973,039
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	25,000,000	25,000,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenue	$ 441,231	$ 364,967	$ 273,499
Cost of revenue	150,986	123,328	96,979
Gross profit	290,245	241,639	176,520
Operating expenses:
Marketing	109,085	82,248	66,771
Product development	74,616	55,083	42,694
General and administrative	91,486	86,180	68,939
Asset impairment charges	3,162	551	0
Total operating expenses	278,349	224,062	178,404
Income (loss) from operations	11,896	17,577	(1,884)
Other income (expense):
Interest expense and amortization of deferred financing costs	(11,130)	(7,204)	(1,526)
Interest and other income	2,394	1,702	324
Net unrealized loss on warrant and other liabilities	0	0	(3,133)
Foreign exchange gain (loss)	29,105	(14,951)	(21,775)
Total other income (expense)	20,369	(20,453)	(26,110)
Income (loss) before income taxes	32,265	(2,876)	(27,994)
Benefit (provision) for income taxes	49,535	(27,025)	(26,069)
Net income (loss)	$ 81,800	$ (29,901)	$ (54,063)
Net income (loss) per share attributable to common stockholders:
Basic (in dollars per share)	$ 0.69	$ (0.26)	$ (0.59)
Diluted (in dollars per share)	$ 0.68	$ (0.26)	$ (0.59)
Weighted average common shares outstanding:
Basic (in shares)	118,538,687	113,562,738	91,122,291
Diluted (in shares)	122,267,673	113,562,738	91,122,291

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 81,800	$ (29,901)	$ (54,063)
Other comprehensive (loss) income:
Cumulative translation adjustment	(24,898)	7,675	14,746
Unrealized gains (losses) on marketable securities, net of tax	47	(8)	(7)
Other comprehensive income	(24,851)	7,667	14,739
Comprehensive income (loss)	$ 56,949	$ (22,234)	$ (39,324)

Consolidated Statements of Chan

Consolidated Statements of Changes in Convertible Preferred Stock and Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred StockSeries A and A-1 preferred stock	Preferred StockSeries B preferred stock	Preferred StockSeries C preferred stock	Preferred StockSeries D and D-1 preferred stock	Preferred StockSeries E preferred stock	Preferred StockSeries 1 preferred stock	Preferred StockSeries F preferred stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss) Income
Convertible preferred stock, beginning balance at Dec. 31, 2014		$ 808	$ 865	$ 3,361	$ 27,870	$ 6,201	$ 1,322	$ 39,785
Convertible preferred stock, beginning balance (in shares) at Dec. 31, 2014		2,363,786	1,128,425	1,222,282	4,215,610	396,727	203,399	11,594,203
Increase (Decrease) in Temporary Equity [Roll Forward]
Convertible preferred stock, conversion of preferred stock upon public offering		$ (808)	$ (865)	$ (3,361)	$ (27,870)	$ (6,201)	$ (1,322)	$ (39,785)
Convertible preferred stock, conversion of preferred stock upon public offering (in shares)		(2,363,786)	(1,128,425)	(1,222,282)	(4,215,610)	(396,727)	(203,399)	(11,594,203)
Convertible preferred stock, ending balance at Dec. 31, 2015		$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Convertible preferred stock, ending balance (in shares) at Dec. 31, 2015		0	0	0	0	0	0	0
Beginning balance at Dec. 31, 2014	$ 67,088								$ 44	$ 103,355	$ (32,377)	$ (3,934)
Beginning balance (in shares) at Dec. 31, 2014									44,180,939
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	9,444									9,444
Exercise of vested options	$ 3,626								$ 2	3,624
Exercise of vested options (in shares)	1,315,735								1,315,735
Exercise of warrants, net of shares withheld	$ 0
Common stock issued through public offering	194,361								$ 14	194,347
Common stock issued through public offering (in shares)									13,333,333
Contribution of stock to Good Work Institute (formerly Etsy.org)	3,200									3,200
Common stock issued through public offering (in shares)									188,235
Stock-based compensation—acquisitions	1,122									1,122
Conversion of liability-classified restricted shares upon vesting	1,755									1,755
Conversion of preferred stock upon public offering	80,212								$ 53	80,159
Conversion of preferred stock upon public offering (in shares)									53,448,243
Conversion of liability-classified warrants upon public offering	5,070									5,070
Excess tax benefit from the exercise of options	3,944									3,944
Other comprehensive income	14,739											14,739
Net income (loss)	(54,063)										(54,063)
Ending balance at Dec. 31, 2015	330,498								$ 113	406,020	(86,440)	10,805
Ending balance (in shares) at Dec. 31, 2015									(112,563,354)
Convertible preferred stock, ending balance at Dec. 31, 2016		$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Convertible preferred stock, ending balance (in shares) at Dec. 31, 2016		0	0	0	0	0	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	13,960									13,960
Exercise of vested options	$ 10,568								$ 3	10,565
Exercise of vested options (in shares)	2,535,620								2,535,620
Vesting of restricted stock units, net of shares withheld	$ (1,258)									(1,258)
Vesting of restricted stock units, net of shares withheld (in shares)									144,651
Exercise of warrants, net of shares withheld	0
Common stock issued through public offering	6,966									6,966
Common stock issued through public offering (in shares)									685,749
Stock-based compensation—acquisitions	1,080									1,080
Retirement of restricted shares	0
Retirement of restricted shares (in shares)									(36,346)
Conversion of liability-classified restricted shares upon vesting	1,942									1,942
Excess tax benefit from the exercise of options	3,235									3,235
Other comprehensive income	7,667											7,667
Net income (loss)	(29,901)										(29,901)
Ending balance at Dec. 31, 2016	344,757								$ 116	442,510	(116,341)	18,472
Ending balance (in shares) at Dec. 31, 2016									(115,973,039)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect on beginning retained earnings	(51,364)									85	(51,449)
Convertible preferred stock, ending balance at Dec. 31, 2017		$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Convertible preferred stock, ending balance (in shares) at Dec. 31, 2017		0	0	0	0	0	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	23,462									23,462
Exercise of vested options	$ 33,838								$ 6	33,832
Exercise of vested options (in shares)	5,760,263								5,760,263
Vesting of restricted stock units, net of shares withheld	$ (6,417)								$ 1	(6,418)
Vesting of restricted stock units, net of shares withheld (in shares)									622,167
Stock repurchase	(10,301)								$ (1)		(10,300)
Stock repurchase (in shares)									(586,231)
Stock-based compensation—acquisitions	3,132									3,132
Conversion of liability-classified restricted shares upon vesting	2,838									2,838
Other comprehensive income	(24,851)											(24,851)
Net income (loss)	81,800										81,800
Ending balance at Dec. 31, 2017	$ 396,894								$ 122	$ 499,441	$ (96,290)	$ (6,379)
Ending balance (in shares) at Dec. 31, 2017									(121,769,238)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net income (loss)	$ 81,800	$ (29,901)	$ (54,063)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Stock-based compensation expense	22,655	13,168	8,981
Stock-based compensation expense—acquisitions	3,904	2,733	1,860
Contribution of stock to Good Work Institute (formerly Etsy.org)	0	0	3,200
Depreciation and amortization expense	27,197	22,525	18,550
Bad debt expense	2,497	1,770	1,780
Foreign exchange (gain) loss	(29,105)	14,951	21,775
Amortization of debt issuance costs	463	184	167
Non-cash interest expense	3,117	5,337	0
Interest on marketable securities	426	914	0
Net unrealized loss on warrant and other liabilities	0	0	3,133
Loss on disposal of assets	520	1,143	1,319
Asset impairment charges	3,162	551	0
Amortization of deferred tax charge	(47,972)	2,194	(4,146)
Amortization of deferred tax charge	0	17,132	17,132
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable	(8,826)	(8,192)	(6,739)
Funds receivable and seller accounts	(13,477)	(10,910)	(9,025)
Prepaid expenses and other current assets	(4,429)	(6,186)	(266)
Other assets	(28)	438	225
Accounts payable	2,837	(3,585)	6,728
Accrued and other current liabilities	3,207	11,193	12,395
Funds payable and amounts due to sellers	13,477	10,910	9,025
Deferred revenue	434	964	1,279
Other liabilities	5,561	2,661	(155)
Net cash provided by operating activities	67,420	49,994	33,155
Cash flows from investing activities
Acquisition of businesses, net of cash acquired	0	(7,880)	0
Purchases of property and equipment	(3,948)	(35,981)	(11,116)
Development of internal-use software	(9,208)	(11,769)	(9,719)
Purchases of marketable securities	(62,348)	(160,504)	(26,040)
Sales of marketable securities	137,340	80,704	23,592
Net cash provided by (used in) investing activities	61,836	(135,430)	(23,283)
Cash flows from financing activities
Proceeds from public offering	0	0	199,467
Repurchase of stock for tax on RSU vesting	(6,417)	(1,258)	0
Repurchase of stock for tax on RSU vesting	(10,301)	0	0
Proceeds from exercise of stock options	33,838	10,568	3,626
Payments on capital lease obligations	(7,798)	(6,086)	(3,377)
Deferred payments on acquisition of business	0	(649)	0
Payments on facility financing obligation	(5,883)	0	0
Payments relating to public offering	0	0	(4,052)
Net cash provided by financing activities	3,439	2,575	195,664
Effect of exchange rate changes on cash	1,155	(6,791)	(3,951)
Net increase (decrease) in cash and cash equivalents	133,850	(89,652)	201,585
Cash and cash equivalents at beginning of period	181,592	271,244	69,659
Cash and cash equivalents at end of period	315,442	181,592	271,244
Supplemental cash flow disclosures:
Cash paid for interest	7,555	2,000	1,346
Cash paid for income taxes	1,003	10,559	7,604
Supplemental non-cash disclosures:
Equipment acquired under capital lease obligations	5,586	5,030	11,657
Stock-based compensation capitalized in development of capitalized software	807	792	463
Additions to development of internal-use software and property and equipment included in accounts payable and accrued expenses	956	2,239	12,721
Non-cash addition to construction in progress related to build-to-suit lease and facility financing obligation	0	0	1,484
Non-cash addition to capitalized public offering costs	0	0	13
Fair value of common stock issued in acquisition	$ 0	$ 6,966	$ 0

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	Note 1—Basis of Presentation and Summary of Significant Accounting Policies Description of Business Etsy, Inc. (the “Company” or “Etsy”) was incorporated in Delaware in February 2006. Etsy is the global marketplace for unique and creative goods. The Company generates revenue primarily from transaction and listing fees, Etsy Payments fees (formerly referred to as Direct Checkout fees), Promoted Listing fees, Shipping Label sales and Pattern by Etsy fees. Initial Public Offering On April 21, 2015, the Company completed an initial public offering (the “IPO”) in which it issued and sold 13,333,333 shares of common stock at a public offering price of $16.00 per share. The Company received net proceeds of $194.4 million after deducting underwriting discounts of $13.9 million and other offering expenses of approximately $5.1 million . These expenses were recorded against the proceeds received from the IPO. Certain selling stockholders sold an additional 5,833,332 shares of common stock in the IPO. The Company did not receive any proceeds from the sale of shares sold by the selling stockholders. Upon the closing of the IPO, all outstanding shares of convertible preferred stock of the Company converted into 53,448,243 shares of common stock. In addition, all outstanding warrants for convertible preferred stock converted into warrants for an aggregate of 203,030 shares of common stock. In connection with the IPO, the Company effected a 1-for-2 reverse split of its common stock on March 25, 2015. The reverse split combined each two shares of the Company’s issued and outstanding common stock into one share of common stock and correspondingly adjusted the conversion prices of the Company's convertible preferred stock. No fractional shares were issued in connection with the reverse split, and fractional shares resulting from the reverse split were rounded down to the nearest whole share. All share, per share and related information presented in the consolidated financial statements and accompanying notes have been retroactively adjusted, where applicable, to reflect the reverse stock split. Basis of Consolidation The consolidated financial statements include the accounts of Etsy and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Reclassifications Certain items in the prior years’ consolidated financial statements have been reclassified to conform to the current year presentation reflected in the consolidated financial statements. Specifically, the Company reclassified $0.6 million previously included in marketing expenses to asset impairment charges on the Consolidated Statements of Operations for the quarter and year ended December 31, 2016 , to conform to the current year presentation. The Company also reclassified $2.2 million and $4.1 million previously included in changes in other liabilities to deferred income taxes on the Consolidated Statements of Cash Flows for the years ended December 31, 2016 and 2015 to conform to the current year presentation. Additionally, the Company reclassified $3.2 million and $3.9 million from cash provided by financing activities to cash provided by operating activities on the Consolidated Statements of Cash Flows for the years ended December 31, 2016 and 2015 , respectively, to conform to the current year presentation upon adoption of Accounting Standards Update (“ASU”) 2016-09, Stock Compensation: Improvements to Employee Share-based Payment Accounting . Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with accounting principles generally accepted in the United States of America (“GAAP”) requires management to make estimates and judgments 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. The accounting estimates that require management’s most difficult and subjective judgments include revenue recognition, income taxes, website development costs and internal-use software, purchase price allocations for business combinations, valuation of goodwill and intangible assets, leases, stock-based compensation and restructuring and other exit costs. The Company evaluates its estimates and judgments on an ongoing basis and revises them when necessary. Actual results may differ from the original or revised estimates. Revenue Recognition The Company's revenue is diversified, generated from a mix of marketplace activities and the services and tools provided to Etsy sellers to help them start, manage, and scale their business. The Company recognizes revenue when all of the following conditions are satisfied: (1) there is persuasive evidence of an arrangement; (2) the service has been provided to the Etsy seller; (3) the collection of fees is reasonably assured; and (4) the amount of fees to be paid by the Etsy seller is fixed or determinable. The Company evaluates whether it is appropriate to recognize revenue on a gross or net basis based upon its evaluation of whether it is the primary obligor in a transaction, has inventory risk and has latitude in establishing pricing and selecting suppliers, among other factors. Marketplace revenue . Marketplace revenue is primarily comprised of the 3.5% transaction fee that an Etsy seller pays for each completed transaction, exclusive of shipping fees charged, and the listing fee of $0.20 she pays for each item she lists on Etsy.com. Transaction fees are recognized when the corresponding transaction is made. Listing fees are recognized ratably over a four -month listing period, unless the item is sold or the seller relists it, at which time any remaining listing fee is recognized. Seller Services revenue . Seller Services revenue consists of fees an Etsy seller pays for the Company's four paid services: Etsy Payments (formerly called Direct Checkout), Promoted Listings, Shipping Labels and Pattern. • Revenue from Etsy Payments consists of fees an Etsy seller pays the Company to process credit, debit and Etsy Gift Card payments. Etsy Payments fees vary between 3 - 4% of the item’s total sale price plus a flat fee per order, depending on the country in which her bank account is located. Etsy Payments fees are based on the item’s total sale price, including shipping. Revenue from Etsy Payments is recognized when the corresponding transaction is consummated. • Revenue from Promoted Listings consists of cost-per-click fees an Etsy seller pays for prominent placement of her listings in search results generated by Etsy buyers in the Company's marketplace. Revenue is recognized when the Promoted Listing is clicked. • Revenue from Shipping Labels consists of fees an Etsy seller pays the Company when she purchases shipping labels through its platform, net of the cost the Company incurs in purchasing those shipping labels. The Company provides its sellers shipping labels from the United States Postal Service, FedEx and Canada Post at discounted pricing due to the volume of purchases through its platform. The Company recognizes Shipping Label revenue when an Etsy seller purchases a shipping label. The Company recognizes Shipping Label revenue on a net basis as it is not the primary obligor in the delivery of these services. • Revenue from Pattern consists of monthly subscription and annual domain registration fees an Etsy seller pays to use the Company's custom website services. The Company recognizes revenue from Pattern ratably over the term of the subscription. Other revenue . Other revenue includes the fees the Company receives from commercial partnerships, which are recognized as earned in accordance with the Company's revenue recognition policy. The following table summarizes revenue by type of service (in thousands): Year Ended 2017 2016 2015 Marketplace $ 179,492 $ 158,204 $ 132,648 Seller Services 258,453 200,857 136,608 Other 3,286 5,906 4,243 Revenue $ 441,231 $ 364,967 $ 273,499 Cost of Revenue Cost of revenue primarily consists of the cost of interchange and other fees for credit card processing services, credit card verification service fees and credit card chargebacks to support Etsy Payments revenue and costs of refunds made to Etsy buyers that the Company is not able to collect from Etsy sellers. Cost of revenue also includes expenses associated with the operation and maintenance of the Company’s platform and data centers, including depreciation and amortization, employee-related costs and hosting and bandwidth costs. Accounts Receivable and Allowance for Doubtful Accounts The Company’s trade accounts receivable are recorded at amounts billed to Etsy sellers and are presented on the Consolidated Balance Sheet net of the allowance for doubtful accounts. The allowance is determined by a number of factors, including age of the receivable, current economic conditions, historical losses and management’s assessment of the financial condition of Etsy sellers. Receivables are written off once they are deemed uncollectible, which may arise when Etsy sellers file for bankruptcy or are otherwise deemed unable to repay the amounts owed to the Company. Estimates of uncollectible accounts receivable are recorded to general and administrative expense. The following table summarizes the allowance activity during the periods indicated (in thousands): Year Ended 2017 2016 2015 Balance as of the beginning of period $ 1,999 $ 2,071 $ 1,841 Bad debt expense 2,497 1,770 1,780 Write-offs, net of recoveries and other adjustments (1,809 ) (1,842 ) (1,550 ) Balance as of the end of period $ 2,687 $ 1,999 $ 2,071 Funds Receivable and Seller Accounts and Funds Payable and Amounts due to Sellers The Company records funds receivable and seller accounts and funds payable and amounts due to sellers as current assets and liabilities, respectively, on the Consolidated Balance Sheet. Funds receivable and seller accounts represent amounts received or expected to be received from Etsy buyers via third-party credit card processors, which flow through an Etsy bank account for payment to Etsy sellers. This cash and related receivable represent the total amount due to sellers, and as such a liability for the same amount is recorded to funds payable and amounts due to Etsy sellers. Property and Equipment Property and equipment, consisting principally of building, computer equipment and leasehold improvements, are recorded at cost. The Company capitalizes construction in progress for build-to-suit lease agreements where we are the owner, for accounting purposes only, during the construction period. Depreciation and amortization begin at the time the asset is placed into service and are recognized using the straight-line method in amounts sufficient to relate the cost of depreciable and amortizable assets to operations over their estimated useful lives. Repairs and maintenance are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation or amortization are removed from the balance sheet and the resulting gain or loss is reflected in operations. When events or changes in circumstances require, the Company assesses the likelihood of recovering the cost of tangible long-lived assets based on its expectations of future profitability, undiscounted cash flows and management’s plans with respect to operations to determine if the asset is impaired and subject to write-off. Measurement of any impairment loss is based on the excess of the carrying value of the asset over the fair value. Website Development and Internal-use Software Costs Costs incurred to develop the Company's website and software for internal-use are capitalized and amortized over the estimated useful life of the software, generally three years. In accordance with authoritative accounting guidance, capitalization of costs to develop software begin when preliminary development efforts are successfully completed, management has authorized and committed project funding and it is probable that the project will be completed and the software will be used as intended. The Company also capitalizes costs related to upgrades and enhancements when it is probable the expenditures will result in additional functionality or will extend the useful life of existing functionality. Costs related to the design or maintenance of website development and internal-use software are expensed as incurred. The Company periodically reviews website development and internal-use software costs to determine whether the projects will be completed, placed in service, removed from service or replaced by other internally developed or third-party software. If the asset is not expected to provide any future use, the asset is retired and any unamortized cost is expensed. If an asset will continue to be used, but the net book value is not expected to be fully recoverable, the asset is impaired to its fair value. When events or changes in circumstances require, the Company assesses the likelihood of recovering the cost of website development and internal-use software costs based on its expectations of future profitability, undiscounted cash flows and our plans with respect to operations to determine if the asset is impaired and subject to write-off. Measurement of any impairment loss is based on the excess of the carrying value of the asset over the fair value. If a cloud computing arrangement includes a software license, then the Company accounts for the software license element of the arrangement consistent with the acquisition of other software licenses. If a cloud computing arrangement does not include a software license, the Company accounts for the arrangement as a service contract. Capitalized website development and internal-use software costs are included in property and equipment within the Consolidated Balance Sheets. Leases The Company leases office space and certain computer equipment in multiple locations under non-cancelable lease agreements. The leases are reviewed for classification as operating, capital or build-to-suit leases. For operating leases, rent is recognized on a straight-line basis over the lease period. For capital leases, the Company records the leased asset with a corresponding liability. Payments are recorded as reductions to the liability with an appropriate interest charge recorded based on the then-outstanding remaining liability. The Company considers the nature of the renovations and the Company’s involvement during the construction period of newly leased office space to determine if it is considered, for accounting purposes only, to be the owner of the construction project during the construction period. If the Company determines that it is the owner of the construction project, it is required to capitalize the fair value of the building as well as the construction costs incurred on its Consolidated Balance Sheet along with a corresponding financing liability (“build-to-suit accounting”). Upon occupancy for build-to-suit leases, the Company assesses whether the circumstances qualify for sales recognition under the sale-leaseback accounting guidance. If the lease meets the sale-leaseback criteria, the Company will remove the asset and related financial obligation from the balance sheet and treat the building lease as an operating lease. If upon completion of construction, the project does not meet the sale-leaseback criteria, the leased property will be treated as a capital lease for financial reporting purposes. In May 2016, the Company took possession of its corporate headquarters in Brooklyn, New York upon substantial completion of the construction phase of the build-out. Upon completion of the project, the Company performed a sale-leaseback analysis pursuant to Accounting Standards Codification (“ASC”) 840 —Leases , to determine the appropriateness of removing the previously capitalized assets from the Consolidated Balance Sheets. The Company concluded that components of “continuing involvement” were evident as a result of this review, precluding the derecognition of the related assets from the Consolidated Balance Sheets. In conjunction with the initiation of the lease in May 2014, the Company also recorded a facility financing obligation equal to the fair market value of the assets received from the landlord. As of December 31, 2017 , the facility financing obligation outstanding was $60.0 million . At the end of the lease term, including exercise of any renewal options, the remaining value of the net facility financing obligation over the net carrying value of the fixed asset will be recognized as a non-cash gain on sale of the property. The Company does not report rent expense for the lease. Rather, rental payments under the lease are recognized as a reduction of the financing obligation and interest expense, and the associated asset capitalized throughout the construction project is depreciated over its estimated useful life. Income Taxes The income tax benefit (provision) is based on income (loss) before income taxes and is accounted for under the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to settle. The effect on deferred tax assets and liabilities of a change in tax rates is recognized as income or expense in the period that includes the enactment date. Management assesses the need for a valuation allowance on a quarterly basis to reduce deferred tax assets to the amounts expected to be realized. The Company accounts for uncertainty in income taxes using a recognition threshold and a measurement attribute for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by the taxing authorities. The amount recognized is measured as the largest amount of benefit that has a greater than 50% likelihood of being realized upon ultimate audit settlement. The Company recognizes interest and penalties, if any, associated with income tax matters as part of the income tax provision and includes accrued interest and penalties with the related income tax liability in the Consolidated Balance Sheet. Business Combinations The Company has completed a number of acquisitions of other businesses in the past and may acquire additional businesses or technologies in the future. The results of businesses acquired in a business combination are included in the Company’s consolidated financial statements from the date of acquisition. The Company allocates the purchase price, which is the sum of the consideration provided and may consist of cash, equity or a combination of the two, in a business combination to the identifiable assets and liabilities of the acquired business at their acquisition date fair values. The excess of the purchase price over the amount allocated to the identifiable assets and liabilities, if any, is recorded as goodwill. Determining the fair value of assets acquired and liabilities assumed requires management to use significant judgment and estimates, including the selection of valuation methodologies, estimates of future revenue and cash flows, discount rates and selection of comparable companies. When the Company issues stock-based or cash awards to an acquired company’s stockholders, the Company evaluates whether the awards are contingent consideration or compensation for post-combination services. The evaluation includes, among other things, whether the vesting of the awards is contingent on the continued employment of the acquired company’s stockholder beyond the acquisition date. If continued employment is required for vesting, the awards are treated as compensation for post-combination services and recognized as expense over the requisite service period. The Company initially recognizes intangible assets at fair value, and amortizes them on a straight-line basis over their estimated useful lives. When circumstances indicate that the carrying value of these assets may not be recoverable, the Company reviews its identifiable amortizable intangible assets for impairment. To date, the assets acquired and liabilities assumed in the Company’s business combinations have primarily consisted of goodwill and finite-lived intangible assets, consisting primarily of developed technologies, customer relationships and trademarks. The estimated fair values and useful lives of identifiable intangible assets are based on many factors, including estimates and assumptions of future operating performance and cash flows of the acquired business, the nature of the business acquired and the specific characteristics of the identified intangible assets. The estimates and assumptions used to determine the fair values and useful lives of identified intangible assets could change due to numerous factors, including market conditions, technological developments, economic conditions and competition. In connection with determination of fair values, the Company may engage independent appraisal firms to assist with the valuation of intangible and certain tangible assets acquired and certain assumed obligations. Acquisition-related transaction costs incurred by the Company are not included as a component of consideration transferred, but are accounted for as an expense in the period in which the costs are incurred. Goodwill Goodwill represents the excess of the aggregate fair value of the consideration transferred in a business combination over the fair value of the assets acquired, net of liabilities assumed. Goodwill is not amortized, but is subject to an annual impairment test. Management has determined that the Company has a single reporting unit and performs its annual goodwill impairment test during the fourth quarter or more frequently if events or changes in circumstances indicate that the goodwill may be impaired. Events or changes in circumstances which could trigger an impairment review include significant changes in the manner of the Company’s use of the acquired assets or the strategy for the Company’s overall business, significant negative industry or economic trends, significant underperformance relative to historical or projected future results of operations, a significant adverse change in the business climate, cost factors that have a negative effect on earnings and cash flows, an adverse action or assessment by a regulator, a sustained decrease in share price, unanticipated competition or a loss of key personnel. The Company has the option to first assess qualitative factors to determine whether the existence of events or circumstances leads to a determination that it is more likely than not that the fair value of the reporting unit is less than its carrying amount. If, after assessing the totality of events or circumstances, the Company determines it is not more likely than not that the fair value of the reporting unit is less than its carrying amount, then additional impairment testing is not required. However, if the Company concludes otherwise, then it is required to perform a quantitative assessment for impairment. The quantitative assessment involves comparing the estimated fair value of the reporting unit with its respective book value, including goodwill. If the estimated fair value exceeds book value, goodwill is considered not to be impaired and no additional steps are necessary. If, however, the book value of the reporting unit exceeds the fair value, an impairment loss is recognized in an amount equal to the excess, not to exceed the total amount of goodwill allocated to that reporting unit. The Company completed a qualitative analysis during the fourth quarter of 2017 . No impairment of goodwill was recorded during the three years ended December 31, 2017 . Intangible Assets Intangible assets are amortized over the estimated useful life of the acquired technology, customer relationships and trademarks, generally three years. When events or changes in circumstances require, the Company assesses the likelihood of recovering the cost of intangible assets based on its expectations of future profitability, undiscounted cash flows and management’s plans with respect to operations to determine if the asset is impaired and subject to write-off. Measurement of any impairment loss is based on the excess of the carrying value of the asset over the fair value. Stock-Based Compensation The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). Stock options and restricted stock units (“RSUs”) are awarded to employees and members of our Board of Directors and are measured at fair value at each grant date. The Company calculates the fair value of stock options on the date of grant using the Black-Scholes option-pricing model and the expense is recognized over the requisite service period for awards expected to vest. Prior to the IPO, the Company utilized equity valuations based on comparable publicly-traded companies, discounted free cash flows, an analysis of the Company's enterprise value and other factors deemed relevant in estimating the fair value of its common stock. Subsequent to the IPO, the Company has used the closing price of its common stock on Nasdaq as the fair value of its common stock. The risk-free rate for periods within the contractual life of the option is based on the U.S. Treasury yield curve in effect at the time of grant. Expected volatilities are based on implied volatilities from market comparisons of certain publicly traded companies and other factors. The expected term of stock options granted has been determined using the simplified method, which uses the midpoint between the vesting date and the contractual term. The fair value of RSUs is determined based on the closing price of the Company's common stock on Nasdaq on the grant date. The requisite service period for stock options and RSUs is generally four years from the date of grant. In the first quarter of 2017, the Company made an accounting policy election to recognize forfeitures as they occur upon adoption of guidance in ASU 2016-09, Compensation—Stock Compensation: Scope of Modification Accounting . In reporting periods prior to 2017, the Company estimated forfeitures at the time of grant and revised in subsequent periods as necessary if actual forfeitures differed from estimates. The Company accounts for stock-based compensation arrangements related to the ALM acquisition in restricted shares subject to a put option that allows the holder of the shares to put the shares back to the Company for cash as liability-classified stock awards. These awards are re-measured at fair value each reporting period, with changes in fair value being charged to the statement of operations. Compensation expense is recognized using a graded vesting methodology for each separately vesting tranche as though the award were, in substance, multiple awards. Unless the put option is exercised, the restricted shares will be reclassified from a liability to an equity classified award upon the termination of the put option at the vesting of each separate tranche. In 2017, all outstanding restricted shares subject to a put option became fully vested and the Company will no longer be required to remeasure these awards at fair value going forward. Cash and Cash Equivalents The Company considers all investments with an original maturity of three months or less at time of purchase to be cash equivalents. Cash restricted by third parties is not considered cash and cash equivalents. Short-term Investments Short-term investments, consisting primarily of corporate bonds, U.S. Government and agency securities and commercial paper with original maturities of greater than three months but less than one year when purchased, are classified as available-for-sale and are reported at fair value using the specific identification method. Unrealized gains and losses are excluded from earnings and reported as a component of other comprehensive income (loss), net of related estimated income tax provisions or benefits. Concentration of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist of cash and cash equivalents, short-term investments and funds receivable and seller accounts. The Company reduces credit risk by placing its cash and cash equivalents with major financial institutions with high credit ratings. At times, such amounts may exceed federally insured limits. In addition, funds receivable are generated primarily with credit card and payment processing companies which management believes are of high credit quality. Fair Value of Financial Instruments Management believes that the fair value of financial instruments, consisting of cash and cash equivalents, short-term investments, accounts receivable, funds receivable and seller accounts, accounts payable and funds payable and seller accounts, approximates carrying value due to the immediate or short-term maturity associated with these instruments. Marketing Marketing expenses largely consist of direct marketing and indirect employee-related expenses to support our marketing initiatives. Direct marketing includes digital marketing, brand marketing, seller lifecycle and growth activities, public relations and communications and marketing partnerships. Digital marketing primarily consists of targeted promotional campaigns through electronic channels, such as product listing ads, search engine marketing, affiliate programs and display advertising which are focused on buyer acquisition and brand marketing. Advertising expenses, which are expensed as incurred, related to direct marketing, included in marketing expenses on the Consolidated Statements of Operations, were $78.4 million , $55.5 million and $46.9 million in the years ended December 31, 2017, 2016 and 2015, respectively. Product development Product development expenses consist primarily of employee-related expenses for engineering, product management, product design and product research activities. Additional expenses include consulting costs related to the development, quality assurance and testing of new technology and enhancement of our existing technology. Net Income (Loss) Per Share The Company follows the two-class method when computing net income (loss) per share as the Company has issued restricted shares that meet the definition of participating securities in connection with the acquisition of Blackbird Technologies, Inc (“Blackbird”) in 2016. The two-class method determines net income (loss) per share for each class of common stock and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common stock and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. The Company will continue to implement the two-class method when computing net income (loss) per share through the end of the three year vesting term for these restricted shares. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding for the period. Diluted net income (loss) per share is computed by dividing net income (loss) for the period by the weighted average number of shares of common stock and potentially dilutive common stock outstanding during the period. The dilutive effect of outstanding options and stock-based compensation awards is reflected in diluted net income (loss) per share by application of the treasury stock method. The calculation of diluted net income (loss) per share excludes all anti-dilutive common shares. For periods in which the Company has reported net losses, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, because dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. Contingencies The Company accrues for loss contingencies when losses become probable and are rea

Business Combinations

Business Combinations	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Business Combinations	Note 2—Business Combinations On September 19, 2016 , the Company acquired all of the outstanding common stock of Blackbird, a machine learning company, for $32.5 million . The Company completed this acquisition to improve the quality and relevance of search on Etsy.com. Total consideration for the acquisition was approximately $15.0 million , consisting of $8.1 million in cash and 513,304 shares of the Company’s common stock with a fair value of $6.9 million on the acquisition date. Additionally, the Company issued 184,230 shares of common stock and restricted stock units (“RSUs”) on the acquisition date with a fair value of $2.5 million which are tied to continuous service with the Company as an employee and are being accounted for as post-combination stock-based compensation expense over a three -year vesting period. The Company agreed to pay up to an additional $8.8 million in cash and issue an aggregate of 460,575 shares of RSUs post-close with a fair value of $6.2 million , both of which are also tied to continuous service with the Company as an employee and are being accounted for as post-combination stock-based and other compensation expense over a three -year vesting period. A portion of the consideration and post-combination compensation is subject to indemnification provisions. The below table summarizes the components of the Blackbird purchase price and allocation of the purchase price at fair value (in thousands): Cash paid $ 8,050 Common shares 6,966 Total purchase consideration $ 15,016 Net working capital $ 81 Developed technology 7,200 Customer relationships 1,250 Goodwill 8,660 Deferred tax liability (2,175 ) Net assets acquired $ 15,016 Included in working capital is approximately $0.2 million of cash acquired. The amounts allocated to developed technology and customer relationships (the acquired intangible assets) total $8.5 million . The acquired identifiable intangible assets are being amortized on a straight-line basis approximating the pattern in which the assets are utilized. Acquired technology intangible assets will amortize over three years and acquired customer relationships were amortized over six months from the acquisition date. The fair value assigned to developed technology was determined primarily by using the cost approach, which estimates the cost to reproduce the asset, adjusted for loss due to functional and economic obsolescence. The fair value of the Company’s customer relationships was determined primarily by using the income approach, which discounts expected future cash flows to present value using estimates and assumptions determined by management. Goodwill recorded in connection with the Blackbird acquisition is primarily attributed to the value of the acquired workforce and their future contribution to Etsy. None of the resulting goodwill is deductible for tax purposes. The Company incurred approximately $0.6 million in acquisition-related costs in the Blackbird acquisition in the year ended December 31, 2016 , included in general and administrative expenses. This acquisition decreased the Company’s consolidated net income in the year ended December 31, 2017 by $9.2 million and contributed $2.4 million to the Company’s consolidated net loss in the year ended December 31, 2016 . The impact to net income in the year ended December 31, 2017 was primarily due to stock-based and other compensation expenses associated with the acquisition of $5.8 million and amortization of intangibles of $3.0 million , included in product development and marketing expenses. The following unaudited pro forma financial information presents the combined operating results of the Company and Blackbird as if the acquisition had occurred on January 1, 2015 . The unaudited pro forma financial information includes the accounting effects of the business combination, including adjustments to the amortization of intangible assets, stock-based and other compensation expenses and professional fees associated with the acquisition. The unaudited pro forma information does not necessarily reflect the actual results that would have been achieved, nor is it necessarily indicative of our future consolidated results. The unaudited pro forma financial information is presented in the table below for the years ended December 31, 2016 and 2015 (in thousands except per share amounts): Year Ended December 31, 2016 2015 Revenue $ 365,786 $ 273,616 Net loss (35,401 ) (65,106 ) Basic and diluted net loss per share (0.31 ) (0.71 )

Restructuring and Other Exit Co

Restructuring and Other Exit Costs	12 Months Ended
	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Restructuring and Other Exit Costs	Note 3—Restructuring and Other Exit Costs On April 30, 2017, the Board of Directors approved a plan to increase efficiency and streamline the Company's cost structure through headcount reductions and a reduction in internal program expenses (the “May Actions”). On June 16, 2017, the Board of Directors approved additional initiatives that were designed to improve focus on key strategic growth opportunities (together with the May Actions, the “Actions”). The Actions included total headcount reductions of 245 positions or 23% of the total workforce as of December 31, 2016, closing A Little Market (“ALM”), a marketplace in France, and closing or consolidating certain international offices. In connection with the Actions, the Company incurred $13.9 million of restructuring and other exit costs for the year ended December 31, 2017 , including $10.2 million of severance charges, $2.7 million of stock modification charges and $1.0 million of other exit costs. The Company expects to incur up to an additional $0.8 million of potential costs, which are expected to be recognized through the first half of 2018. The remaining range of expected costs relates primarily to uncertainty in the amount of exit costs that will be recognized in connection with the ultimate disposition of one of the Company's international offices. The following table displays restructuring and other exit costs recorded related to the Actions and a rollforward of the charges to the accrued balance as of December 31, 2017 (in thousands): Severance Charge Stock-Based Compensation Other Exit Costs Total Balance, December 31, 2016 $ — $ — $ — $ — Total restructuring and other exit costs 8,972 1,668 620 11,260 Costs charged against equity/assets — (1,668 ) — (1,668 ) Cash payments (2,110 ) — (278 ) (2,388 ) Balance, June 30, 2017 6,862 — 342 7,204 Total restructuring and other exit costs 871 965 (70 ) 1,766 Costs charged against equity/assets — (965 ) — (965 ) Cash payments (4,385 ) — (180 ) (4,565 ) Balance, September 30, 2017 3,348 — 92 3,440 Total restructuring and other exit costs 361 68 442 871 Costs charged against equity/assets — (68 ) (286 ) (354 ) Cash payments (2,401 ) — (214 ) (2,615 ) Balance, December 31, 2017 $ 1,308 $ — $ 34 $ 1,342 The Company expects remaining accrued balances related to restructuring and other exit costs as of December 31, 2017 to be paid in the first half of 2018. Total restructuring and other exit costs included in the Consolidated Statements of Operations are as follows (in thousands): Year Ended 2017 2016 2015 Cost of revenue $ 738 $ — $ — Marketing 2,950 — — Product development 3,232 — — General and administrative 6,977 — — Total restructuring and other exit costs $ 13,897 $ — $ —

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 4—Fair Value Measurements The Company has characterized its investments in marketable securities, based on the priority of the inputs used to value the investments, into a three-level fair value hierarchy. The fair value hierarchy gives the highest priority to quoted prices in active markets for identical assets or liabilities (Level 1), and lowest priority to unobservable inputs (Level 3). If the inputs used to measure the investments fall within different levels of the hierarchy, the categorization is based on the lowest level input that is significant to the fair value measurement of the investment. Investments recorded in the accompanying Consolidated Balance Sheet are categorized based on the inputs to valuation techniques as follows: Level 1—These are investments where values are based on unadjusted quoted prices for identical assets in an active market that the Company has the ability to access. Level 2—These are investments where values are based on quoted market prices in markets that are not active or model derived valuations in which all significant inputs are observable in active markets. Level 3—These are liabilities where values are derived from techniques in which one or more significant inputs are unobservable. The following are the major categories of assets and liabilities measured at fair value on a recurring basis as of the dates indicated (in thousands): As of December 31, 2017 Level 1 Level 2 Level 3 Total Asset Cash equivalents: Commercial paper $ — $ 11,290 $ — $ 11,290 Money market funds 204,867 — — 204,867 U.S. Government and agency securities 24,989 — — 24,989 229,856 11,290 — 241,146 Short-term investments: Commercial paper — 2,998 — 2,998 Corporate bonds — 12,748 — 12,748 U.S. Government and agency securities 9,362 — — 9,362 9,362 15,746 — 25,108 Funds receivable and seller accounts: Money market funds 14,144 — — 14,144 14,144 — — 14,144 $ 253,362 $ 27,036 $ — $ 280,398 As of December 31, 2016 Level 1 Level 2 Level 3 Total Asset Cash equivalents: Commercial paper $ — $ 2,997 $ — $ 2,997 Money market funds 98,161 — — 98,161 U.S. Government and agency securities 1,950 — — 1,950 100,111 2,997 — 103,108 Short-term investments: Commercial paper — 17,146 — 17,146 Corporate bonds — 33,303 — 33,303 U.S. Government and agency securities 50,045 — — 50,045 50,045 50,449 — 100,494 $ 150,156 $ 53,446 $ — $ 203,602 Liability Post-combination compensation classified as liability $ — $ — $ 2,067 $ 2,067 $ — $ — $ 2,067 $ 2,067 Level 1 instruments include money market funds and AA-rated U.S. Government and agency securities, which are valued based on inputs including quotes from broker-dealers or recently executed transactions in the same or similar securities. Level 2 instruments include fixed-income funds consisting of investments in commercial paper and corporate bonds, which are valued based on quoted market prices in markets that are not active or model derived valuations in which all significant inputs are observable in active markets. Level 3 instruments include post-combination compensation classified as a liability in connection with the acquisition of A Little Market (“ALM”). The post-combination compensation was classified as a liability due to its affiliation with a related put option, which expired upon vesting of the underlying consideration in the second quarter of 2017, and its fair value was previously determined based on the fair value of the Company's common stock at the period-end reporting date, with adjustments included in general and administrative expenses. The table below provides a reconciliation of the beginning and ending balances for the liabilities measured at fair value using significant unobservable inputs (Level 3) (in thousands): Year Ended 2017 2016 Balance at beginning of period $ 2,067 $ 2,357 Changes to liability-classified stock awards 771 1,652 Conversion of liability-classified instruments to equity (2,838 ) (1,942 ) Balance at end of period $ — $ 2,067

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	Note 5—Marketable Securities Short-term investments and certain cash equivalents consist of marketable securities that are available-for-sale. The cost and fair value of available-for-sale securities were as follows as of the dates indicated (in thousands): Cost Gross Gross Fair Value December 31, 2017 Cash equivalents: Commercial paper $ 11,290 $ — $ — $ 11,290 U.S. Government and agency securities 24,990 (1 ) — 24,989 36,280 (1 ) — 36,279 Short-term investments: Commercial paper 2,998 — — 2,998 Corporate bonds 12,754 (6 ) — 12,748 U.S. Government and agency securities 9,352 (1 ) 11 9,362 25,104 (7 ) 11 25,108 $ 61,384 $ (8 ) $ 11 $ 61,387 December 31, 2016 Cash equivalents: Commercial paper $ 2,997 $ — $ — $ 2,997 2,997 — — 2,997 Short-term investments: Commercial paper 17,146 — — 17,146 Corporate bonds 33,318 (16 ) 1 33,303 U.S. Government and agency securities 50,059 (15 ) 1 50,045 100,523 (31 ) 2 100,494 $ 103,520 $ (31 ) $ 2 $ 103,491 The Company’s investments in marketable securities consist primarily of investments in AA-rated U.S. Government and agency securities and fixed-income funds. When evaluating investments for other-than-temporary impairment, the Company reviews factors such as length of time and extent to which fair value has been below cost basis, the financial condition of the issuer and the Company’s ability and intent to hold the investment for a period of time, which may be sufficient for anticipated recovery in market value. The Company evaluates fair values for each individual security in the investment portfolio.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property and Equipment	Note 6—Property and Equipment Property and equipment consisted of the following as of the dates indicated (in thousands): As of Estimated useful lives 2017 2016 Computer equipment 3 years $ 35,587 $ 30,378 Furniture and equipment 2 - 4 years 6,194 5,920 Software 1 - 3 years 908 856 Leasehold improvements Shorter of life of asset or lease term 10,929 10,155 Building 25 years 81,892 81,957 Website development 3 years 48,333 43,294 183,843 172,560 Less: Accumulated depreciation and amortization 66,226 46,153 $ 117,617 $ 126,407 Depreciation and amortization expense on property and equipment was $23.8 million , $19.2 million and $16.3 million for the years ended December 31, 2017, 2016 and 2015 , respectively, which includes amortization expense for equipment acquired under capital leases of $7.7 million , $6.3 million and $3.8 million for the years ended December 31, 2017, 2016 and 2015 , respectively. The gross balance of leased equipment as of December 31, 2017 and 2016 was $27.7 million and $22.3 million , respectively. The related accumulated amortization of equipment under capital leases was $18.6 million and $10.9 million at December 31, 2017 and 2016 , respectively. The following table summarizes capitalized website development and internal-use software activities during the periods indicated (in thousands): Year Ended 2017 2016 Balance as of the beginning of the period $ 43,294 $ 33,469 Additions to website development, excluding stock-based compensation 10,028 11,769 Additions to website development—stock-based compensation 807 792 Less: Retirements 625 2,736 Less: Impairments 5,171 — 48,333 43,294 Less: Accumulated amortization balance as of the beginning of the period 24,155 19,676 Amortization Expense 8,209 6,333 Less: Retirements 364 1,854 Less: Impairments 2,009 — Accumulated amortization balance as of the end of the period 29,991 24,155 $ 18,342 $ 19,139 For the years ended December 31, 2017, 2016 and 2015 , the Company recorded amortization expense relating to capitalized website development and internal-use software of $8.2 million , $6.3 million and $7.3 million , respectively. The loss on write-off for capitalized website development and internal-use software assets that were retired during the years ended December 31, 2017, 2016 and 2015 was $0.3 million , $0.9 million and $1.3 million , respectively. The Company recognized a $3.2 million impairment loss related to capitalized website development and internal-use software during the year ended December 31, 2017 , included in asset impairment charges. During the fourth quarter of 2017, the Company made the decision to discontinue certain product offerings, including Etsy Studio and Etsy Manufacturing, which was an indicator that the carrying amount of certain capitalized website development and internal-use software assets may not be recoverable. The Company prepared an undiscounted cash flow analysis and determined that the values for these assets exceeded the expected future cash flows and impaired the remaining book values based on a negative present value of projected undiscounted cash flows.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Note 7—Goodwill and Intangible Assets The following table summarizes the changes in the carrying amount of goodwill for the periods indicated (in thousands): Year Ended 2017 2016 Balance as of the beginning of the period $ 35,657 $ 27,752 Acquisitions(1) — 8,660 Foreign currency translation adjustments 2,884 (755 ) Balance as of the end of the period $ 38,541 $ 35,657 (1) Includes goodwill as a result of the Blackbird Technologies acquisition. See “ Note 2—Business Combinations ” for more information. The Company did not recognize any goodwill impairments during the years ended December 31, 2017, 2016 and 2015 . At December 31, 2017 and 2016 , the gross book value and accumulated amortization of intangible assets were as follows (in thousands): As of December 31, 2017 As of December 31, 2016 Gross book Accumulated Net book Gross book Accumulated Net book Technology $ 7,200 $ (3,100 ) $ 4,100 $ 10,466 $ (3,536 ) $ 6,930 Customer relationships — — — 1,250 (673 ) 577 Intangible assets, net $ 7,200 $ (3,100 ) $ 4,100 $ 11,716 $ (4,209 ) $ 7,507 (1) Excludes the gross book value and accumulated amortization of fully amortized intangibles. The Company acquired intangible assets valued at $8.5 million in the Blackbird acquisition on September 19, 2016 . The Company acquired intangible assets valued at $4.1 million and $2.8 million in the ALM and Jarvis Labs, Inc. (“Grand St.”) acquisitions in June and April 2014. Amortization expense for the years ended December 31, 2017, 2016 and 2015 was $3.4 million , $3.3 million and $2.2 million , respectively. The Company did not recognize any intangible asset impairment losses in the year ended December 31, 2017 . The Company recognized a $0.6 million intangible asset impairment loss during the year ended December 31, 2016 , included in asset impairment charges. During the fourth quarter of 2016, the Company determined that there were indicators present that the carrying amount of intangible assets acquired in the ALM and Grand St. acquisitions may not be recoverable. The Company prepared an undiscounted cash flow analysis and determined that intangible assets for customer relationships and trademarks acquired in the ALM and Grand St. acquisitions were not recoverable. The Company used the income approach to determine the fair value of intangible assets and concluded that these assets were fully impaired. Based on amounts recorded at December 31, 2017 , the Company estimates intangible asset amortization expense in each of the years ending December 31 as follows (in thousands): 2018 $ 2,400 2019 1,700 Thereafter — Total amortization expense $ 4,100

Debt

Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Debt	Note 8—Debt Credit Agreement The Company terminated the senior secured revolving credit facility pursuant to a Revolving Credit and Guaranty Agreement with several lenders (the “Credit Agreement”) effective as of November 21, 2017. As of the date of termination, there were no borrowings outstanding under the Credit Agreement and we incurred no additional fees as a result of early termination. In May 2014 , the Company entered into a $35.0 million Credit Agreement. In March 2015, the Company amended the Credit Agreement to increase the credit facility to $50.0 million. In December 2015, the Company amended the Credit Agreement to clarify certain provisions relating to permitted investments and to make other immaterial updates. The amended Credit Agreement included a letter of credit sublimit of $10.0 million and a swingline loan sublimit of $15.0 million. The Credit Agreement, as amended, would have expired in May 2019.

Warrants

Warrants	12 Months Ended
	Dec. 31, 2017
Temporary Equity Disclosure [Abstract]
Warrants	Note 9—Warrants As of December 31, 2017 and 2016, the Company did not have any outstanding warrants. In May 2016, the Company issued 80,011 shares of common stock upon the net exercise of warrants to purchase 97,931 shares of common stock with a weighted-average exercise price of $1.62 per share and a weighted-average fair market value of common stock at the date of exercise of $8.88 . The warrant holders exercised this warrant in a cashless transaction and 17,920 shares were forfeited to the Company as payment of the exercise price. During 2015 upon the closing of the IPO, all outstanding warrants for preferred stock were converted into warrants for 203,030 shares of common stock. The warrants were revalued at the opening stock price of $24.97 on April 21, 2015, the closing date of the IPO, and $5.1 million was reclassified from liabilities to equity on that date. In October 2015, the Company issued 96,869 shares of common stock upon the net exercise of warrants to purchase 105,099 shares of common stock with a weighted-average exercise price of $1.03 per share and a weighted-average fair market value of common stock at the date of exercise of $12.90 . The warrant holders exercised this warrant in a cashless transaction and 8,230 shares were forfeited to the Company as payment of the exercise price. The Company did not record any unrealized gains or losses from the remeasurement of the warrants to fair value in the years ended December 31, 2017 and 2016 . During the year ended December 31, 2015 , the Company recorded an unrealized loss of $3.1 million from the remeasurement of the warrants to fair value.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	Note 10—Stockholders’ Equity At December 31, 2017 and 2016 , the authorized capital stock of the Company included 1,400,000,000 shares of common stock. At December 31, 2017 and 2016 there were 25,000,000 shares of preferred stock authorized. Common Stock At December 31, 2017 and 2016 there were 121,769,238 and 115,973,039 shares of common stock issued and outstanding, respectively. Holders of common stock are entitled to one vote per share. Holders of common stock are not entitled to receive dividends unless declared by the Board of Directors. No dividends have been declared through December 31, 2017 . The common stock has a $0.001 par value. Convertible Preferred Stock Upon the closing of the IPO on April 21, 2015, all outstanding shares of convertible preferred stock were converted into 53,448,243 shares of common stock. As of December 31, 2017, 2016 and 2015, there was no convertible preferred stock outstanding. Common Stock Issuances In the year ended December 31, 2016 , the Company issued a total of 685,749 shares of common stock in connection with the acquisition of Blackbird, of which 513,304 shares with an aggregate fair value of $6.9 million on the applicable acquisition date is included in the purchase price and 172,445 shares with an aggregate fair value of $2.3 million on the applicable acquisition date is tied to continued employment with the Company and is being accounted for as post-combination compensation expense. Share Repurchase Program In November 2017, the Board of Directors approved a stock repurchase program that enables the Company to repurchase up to $100 million of its common stock. The program does not have a time limit and may be modified, suspended or terminated at any time by the Board of Directors. The number of shares repurchased and the timing of repurchases will depend on a number of factors, including, but not limited to, stock price, trading volume and general market conditions, along with Etsy’s working capital requirements, general business conditions and other factors. Under the stock repurchase program, the Company may purchase shares of its common stock through various means, including open market transactions, privately negotiated transactions, tender offers or any combination thereof. In addition, open market repurchases of common stock may be made pursuant to trading plans established pursuant to Rule 10b5-1 under the Securities Exchange Act of 1934, as amended, which would permit common stock to be repurchased at a time that the Company might otherwise be precluded from doing so under insider trading laws or self-imposed trading restrictions. The following table summarizes the Company's share repurchase activity, excluding shares withheld to satisfy tax withholding obligations in connection with the vesting of employee restricted stock units (in thousands except share and per share amounts): Shares Repurchased Average Price Paid per Share (1) Value of Shares Repurchased Remaining Amount Authorized Balance as of November 17, 2017 — $ — $ — $ 100,000 Repurchases of common stock for the three months ended: December 31, 2017 586,231 17.57 10,301 (10,301 ) Balance as of December 31, 2017 586,231 $ 17.57 $ 10,301 $ 89,699 (1) Average price paid per share excludes broker commissions. All repurchases were made using cash resources.

Stock-based Compensation

Stock-based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based Compensation	Note 11—Stock-based Compensation The Company's 2015 Equity Incentive Plan (the “2015 Plan”) was adopted by its Board of Directors and approved by stockholders in March 2015. The 2015 Plan became effective immediately upon adoption although no awards were made under it until the effective date of the IPO. The 2015 Plan replaced the 2006 Stock Plan, and no further grants were made under the 2006 Stock Plan as of the effective date of the IPO. Under the 2006 Stock Plan, incentive and nonqualified stock options or rights to purchase common stock were granted to eligible participants. Options were generally granted for a term of 10 years and generally vested 25% after the first year of service and ratably each month over the remaining 36 -month period contingent on continued employment with the Company on each vesting date. The 2015 Plan provides for the grant of incentive stock options, non-statutory stock options, stock appreciation rights, restricted stock, restricted stock units (“RSUs”) and performance cash awards to employees, directors and consultants. Beginning in 2016, the number of shares available for issuance under the 2015 Plan may be increased annually by an amount equal to the lesser of 7,050,000 shares of common stock, 5% of the outstanding shares of common stock as of the last day of the immediately preceding fiscal year, or such other amount as determined by the Company's Board of Directors. The Board of Directors approved an increase of 6,088,461 , 5,798,651 and 2,814,083 shares available for issuance under the 2015 Plan as of January 2, 2018, January 3, 2017 and January 4, 2016 , respectively. Any awards issued under the 2015 Plan that are forfeited by the participant will become available for future grant under the 2015 Plan. The number of shares of the Company’s common stock initially reserved for issuance under the 2015 Plan equaled the sum of 14,100,000 shares plus up to 12,653,075 shares reserved for issuance or subject to outstanding awards under the 2006 Stock Plan. At December 31, 2017 , 23,347,913 shares were authorized under the 2015 Plan and 14,355,379 shares were available for future grant. In the first quarter of 2017, the Company made an accounting policy election to recognize forfeitures as they occur upon adoption of guidance in ASU 2016-09, Stock Compensation: Improvements to Employee Share-based Payment Accounting . In reporting periods prior to 2017, the Company estimated forfeitures at the time of grant and revised in subsequent periods as necessary if actual forfeitures differed from estimates. In the year ended December 31, 2017 , the Company granted nonqualified stock options and RSUs to eligible participants. Options were generally granted for a term of 10 years . For both options and RSUs, vesting is typically over a four -year period and is contingent upon continued employment with the Company on each vesting date. In general, for newly-hired employees, options vest 25% after the first year of service and ratably each month over the remaining 36 -month period. In general, for current employees who receive an additional grant, options vest ratably each month over a 48 -month period. In general, for newly-hired employees, RSUs vest 25% after the first year following the vesting commencement date, which is the first day of the fiscal quarter closest to the date of grant, and then vest ratably each quarter over the remaining 12 -quarter period. In general, for current employees who receive an additional grant, RSUs vest ratably each quarter over a 16 -quarter period following the vesting commencement date, which is the first day of the fiscal quarter closest to the date of grant . The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model using the inputs below. Prior to the IPO, the Company utilized equity valuations based on comparable publicly-traded companies, discounted free cash flows, an analysis of the Company's enterprise value and other factors deemed relevant in estimating the fair value of its common stock. Subsequent to the IPO, the Company has used the closing price of its common stock on Nasdaq as the fair value of its common stock. The risk-free rate for periods within the contractual life of the option is based on the U.S. Treasury yield curve in effect at the time of grant for time periods that approximate the expected life of the option awards. Expected volatilities are based on implied volatilities from market comparisons of certain publicly traded companies and other factors. The expected term of stock options granted has been determined using the simplified method, which uses the midpoint between the vesting date and the contractual term. The requisite service period is generally four years from the date of grant. The fair value of RSUs is determined based on the closing price of the Company's common stock on Nasdaq on the grant date. The fair value of options granted in each year using the Black-Scholes pricing model has been based on the following assumptions: Year Ended 2017 2016 2015 Volatility 41.7% - 44.2% 38.6% - 44.6% 40.4% - 45.0% Risk-free interest rate 1.9% - 2.2% 1.1% - 2.1% 1.3% - 1.9% Expected term (in years) 5.5 - 6.3 5.5 - 6.3 5.5 - 6.1 Dividend rate —% —% —% The following table summarizes the activity for the Company’s options (in thousands except share and per share amounts): Shares Weighted-Average Weighted-Average Aggregate Outstanding at December 31, 2014 11,525,279 $ 5.34 7.57 $ 134,386 Granted 1,660,170 16.19 Exercised (1,315,735 ) 2.76 Forfeited/Canceled (800,855 ) 9.94 Outstanding at December 31, 2015 11,068,859 6.94 7.01 31,932 Granted 1,700,234 9.35 Exercised (2,535,620 ) 4.17 Forfeited/Canceled (893,906 ) 9.51 Outstanding at December 31, 2016 9,339,567 7.89 6.64 43,613 Granted 5,887,183 11.04 Exercised (5,760,263 ) 5.87 Forfeited/Canceled (1,518,548 ) 11.36 Outstanding at December 31, 2017 7,947,939 11.02 7.93 74,996 Total exercisable at December 31, 2017 2,294,818 10.48 4.81 22,912 The following table summarizes the weighted average grant date fair value of options granted, intrinsic value of options exercised and fair value of awards vested in periods indicated (in thousands except per share amounts): Year Ended December 31, 2017 2016 2015 Weighted average grant date fair value of options granted $ 4.85 $ 4.03 $ 6.89 Intrinsic value of options exercised 52,693 19,130 15,148 Fair value of awards vested 19,826 9,533 8,337 The total unrecognized compensation expense at December 31, 2017 was $23.7 million , which will be recognized over a weighted-average period of 3.21 years . The following table summarizes the activity for the Company’s unvested RSUs: Shares Weighted-Average Unvested at December 31, 2014 — $ — Granted 407,368 13.78 Vested — — Forfeited/Canceled (11,522 ) 16.76 Unvested at December 31, 2015 395,846 13.70 Granted 3,200,297 10.29 Vested (255,868 ) 10.64 Forfeited/Canceled (205,094 ) 10.15 Unvested at December 31, 2016 3,135,181 10.70 Granted 2,360,315 12.17 Vested (1,072,321 ) 10.44 Forfeited/Canceled (1,348,928 ) 10.56 Unvested at December 31, 2017 3,074,247 11.98 The total unrecognized compensation at December 31, 2017 was $30.1 million , which will be recognized over a weighted-average period of 2.71 years . Total stock-based compensation expense included in the Consolidated Statements of Operations is as follows (in thousands): Year Ended 2017 2016 2015 Cost of revenue $ 1,739 $ 1,057 $ 871 Marketing 1,933 971 560 Product development 8,274 5,079 2,860 General and administrative 14,613 8,794 6,550 Total stock-based compensation expense $ 26,559 $ 15,901 $ 10,841 The total stock-based compensation expense in the years ended December 31, 2017, 2016 and 2015 includes $3.9 million , $2.7 million and $1.9 million , in acquisition-related stock-based compensation expense, respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Note 12—Income Taxes The following are the domestic and foreign components of the Company’s income (loss) before income taxes (in thousands): Year Ended 2017 2016 2015 Domestic $ (16,583 ) $ 25,910 $ 25,627 Foreign 48,848 (28,786 ) (53,621 ) Income (loss) before income taxes $ 32,265 $ (2,876 ) $ (27,994 ) The income tax (benefit) provision is comprised of the following (in thousands): Year Ended 2017 2016 2015 Current: Federal $ (6,397 ) $ 22,084 $ 24,524 State 79 2,623 3,843 Foreign 476 580 579 Total current (5,842 ) 25,287 28,946 Deferred: Federal (34,948 ) 2,008 (2,863 ) State (8,778 ) (247 ) 108 Foreign 33 (23 ) (122 ) Total deferred (43,693 ) 1,738 (2,877 ) Total income tax (benefit) provision $ (49,535 ) $ 27,025 $ 26,069 The current tax expense listed above does not reflect income tax benefits of $3.2 million and $3.9 million for the years ended December 31, 2016 and 2015 , respectively, related to excess tax deductions on share-based compensation because these benefits were recorded directly to additional paid-in capital. Beginning in the first quarter of 2017, the Company adopted ASU 2016-09, Stock Compensation: Improvements to Employee Share-based Payment Accounting, and subsequently recorded excess tax deductions on share-based compensation as income tax benefit in its income statement. Please refer to “ Note 1—Basis of Presentation and Summary of Significant Accounting Policies ” for additional detail regarding the adoption of this accounting standard and its impact on the consolidated financial statements. A reconciliation of the income tax (benefit) provision at the U.S. federal statutory income tax rate of 35% to the Company’s total income tax (benefit) provision is as follows (in thousands): Year Ended 2017 2016 2015 Income tax benefit at federal statutory rate $ 11,308 $ (1,007 ) $ (9,798 ) State and local taxes net of federal benefit (691 ) 1,545 2,575 Foreign income tax rate differential (11,878 ) 5,849 11,584 Stock-based compensation (12,584 ) 1,412 1,571 Net unrealized loss on warrant and other liabilities — — 1,097 Non-deductible items 168 267 1,314 Uncertain tax positions 789 4,033 5,523 Return to provision adjustment 167 (498 ) (25 ) Non-deductible acquisition costs — 199 10 Change in valuation allowance (4,673 ) 4,911 7,957 Research and development credit (1,098 ) (2,170 ) (7,684 ) Deferred charge on restructuring — 12,168 12,168 U.S. tax reform (31,063 ) — — Other 20 316 (223 ) Total income tax (benefit) provision $ (49,535 ) $ 27,025 $ 26,069 The primary driver of the income tax benefit for the year ended December 31, 2017 was the impact on deferred taxes from the reduction in the U.S. federal corporate tax rate beginning in 2018. On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the “Act”) was signed into law, which, among other items, reduced the corporate income tax rate from 35% to 21%. As a result, our deferred taxes and certain unrecognized tax benefits at December 31, 2017 have been revalued at the reduced 21% rate. The revaluation resulted in a benefit for income taxes of approximately $31.1 million for the year ended December 31, 2017 . The secondary driver of the income tax benefit for the year ended December 31, 2017 was the recognition of excess tax benefits from stock-based compensation as a result of the adoption of ASU 2016-09, Stock Compensation: Improvements to Employee Share-based Payment Accounting in the first quarter of 2017. As a result of this updated guidance, we recorded $12.8 million of excess tax benefits, rather than additional paid-in capital, for the year ended December 31, 2017 . Deferred income taxes reflect the net tax effect of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company’s deferred tax assets (liabilities) are as follows (in thousands): As of December 31, 2017 2016 Deferred tax assets: Net operating loss carryforwards $ 17,431 $ 13,084 Research and development credit carryforwards 3,597 898 Stock-based compensation expense 3,776 5,692 Accrued VAT liability 42 68 Alternative minimum tax credit 274 274 Allowance for doubtful accounts 384 611 Deferred rent 573 644 Accrued vacation 623 1,035 Unrealized loss on foreign currency 527 — Other, net 1,691 1,418 Total deferred tax assets 28,918 23,724 Less valuation allowance 11,021 13,839 Total net deferred tax asset 17,897 9,885 Deferred tax liabilities: Depreciation (6,850 ) (6,618 ) Global corporate restructuring liability (33,783 ) (64,460 ) Unrealized gain on foreign currency — (1,059 ) Other liabilities (891 ) (2,816 ) Total deferred tax liabilities (41,524 ) (74,953 ) Net deferred tax liabilities $ (23,627 ) $ (65,068 ) The Company anticipates generating federal and state income tax NOL carryforwards as a result of its 2017 activity. The NOL deferred tax asset balance additionally includes losses in certain foreign jurisdictions that are currently subject to a valuation allowance. As of December 31, 2017 and 2016 , the Company had approximately $0.3 million and $0.3 million , respectively, of federal alternative minimum tax credits, which may be carried forward indefinitely. As of December 31, 2017 and 2016 , the Company had $3.6 million and $0.9 million , respectively, of federal research and development tax credit carryforwards which will begin to expire in 2035 if unused. The Company has not completed its accounting for the income tax effects of certain elements of the Act. The Act creates a new requirement that certain income such as Global Intangible Low-Taxed Income (“GILTI”) earned by a controlled foreign corporation (“CFC”) must be included in the gross income of its U.S. parent. Because of the complexity of the new GILTI and Base Erosion and Anti-abuse Tax (“BEAT”) rules, the Company is continuing to evaluate these provisions of the Act and whether taxes due on future U.S. inclusions related to GILTI and BEAT should be recorded as a current-period expense when incurred, or factored into the Company's measurement of its deferred taxes. As a result, an estimate of the tax expense or benefit related to these items for the period ending December 31, 2017 has not been included. The Company assesses the likelihood of its ability to realize the benefit of its deferred tax assets in each jurisdiction by evaluating all relevant positive and negative evidence. To the extent the Company determines that some or all of its deferred tax assets are not more likely than not to be realized, it establishes a valuation allowance. For the year ended December 31, 2017 , the Company determined that the existence of a three -year cumulative loss incurred in certain foreign jurisdictions, inclusive of 2017 , constituted sufficiently strong negative evidence to warrant the maintenance of a valuation allowance. As a result, a valuation allowance of $11.0 million as of December 31, 2017 has been recorded against certain of the Company’s deferred tax assets. The amount of the deferred tax assets considered realizable is $17.9 million . The following table summarizes the valuation allowance activity for the periods indicated (in thousands): Year Ended 2017 2016 2015 Balance as of the beginning of period $ 13,839 $ 9,540 $ 1,892 Additions charged to expense — 4,886 7,983 Deletions credited to expense (4,691 ) — — Currency translation 1,873 (587 ) (335 ) Balance as of the end of period $ 11,021 $ 13,839 $ 9,540 The Company has not recorded deferred income taxes and withholding taxes with respect to undistributed earnings from its non-U.S. subsidiaries as such earnings are intended to be reinvested indefinitely. The amount of undistributed earnings of non-U.S. subsidiaries at December 31, 2017 , as well as the related deferred income tax, if any, is not material. The following table summarizes the unrecognized tax benefit activity for the periods indicated (in thousands): As of December 31, 2017 2016 2015 Balance as of the beginning of period $ 23,574 $ 22,229 $ 398 Additions based on tax positions related to the current year 732 1,071 21,797 Additions for tax positions of prior years 118 274 34 Reductions for tax provisions of prior years (7,411 ) — — Balance as of the end of period $ 17,013 $ 23,574 $ 22,229 The amount of unrecognized tax benefits included within other liabilities on the Consolidated Balance Sheets as of December 31, 2017, 2016 and 2015 are $17.0 million , $23.6 million and $22.2 million , respectively. The total amount of unrecognized tax benefits that, if recognized, would favorably affect the effective tax rate is $17.0 million at December 31, 2017 . In January 2015, the Company implemented an updated global corporate structure to more closely align with its global operations and future expansion plans outside of the United States. The new structure changed how the Company uses its intellectual property and implemented certain intercompany arrangements. The Company believes this may eventually result in a reduction in its overall effective tax rate and other operational efficiencies. The revised structure resulted in the setup of a deferred tax liability in the amount of $66.0 million on the taxable gain created in the transaction. Concurrently, the Company recorded an asset of $66.0 million for the deferred tax charge representing the future income tax on the gain, which would have been amortized into income tax expense through 2019. During the first quarter of 2017, the Company adopted ASU 2016-16, Income Taxes: Intra-entity Transfers of Assets other than Inventory, resulting in a cumulative adjustment to retained earnings for the unamortized balance of the deferred tax charge at December 31, 2016. Please refer to “ Note 1—Basis of Presentation and Summary of Significant Accounting Policies ” for additional detail regarding the adoption of this accounting standard and its impact on the consolidated financial statements. The Company is subject to taxation in the United States, New York, and various other states and foreign jurisdictions. As of December 31, 2017 , tax year 2014 and later remain open to examination.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	Note 13— Net Income (Loss) Per Share The following table presents the calculation of basic and diluted net income (loss) per share for periods presented (in thousands except share and per share amounts): Year Ended 2017 2016 2015 Numerator: Net income (loss) $ 81,800 $ (29,901 ) $ (54,063 ) Net income (loss) allocated to participating securities under the two-class method (80 ) — — Net income (loss) applicable to common stockholders—basic 81,720 (29,901 ) (54,063 ) Dilutive effect of net income allocated to participating securities under the two-class method 80 — — Change in fair value of liability classified restricted stock 771 — — Net income (loss) applicable to common stockholders—diluted $ 82,571 $ (29,901 ) $ (54,063 ) Denominator: Weighted average common shares outstanding—basic (1) 118,538,687 113,562,738 91,122,291 Common equivalent shares from options to purchase common stock and restricted stock units 2,498,448 — — Dilutive effect of assumed conversion of restricted stock units 1,177,799 — — Diluted effective of assumed conversion of restricted stock from acquisition 52,739 — — Weighted average common shares outstanding—diluted 122,267,673 113,562,738 91,122,291 Net income (loss) per share applicable to common stockholders—basic $ 0.69 $ (0.26 ) $ (0.59 ) Net income (loss) per share applicable to common stockholders—diluted $ 0.68 $ (0.26 ) $ (0.59 ) (1) 114,963 shares of unvested stock are considered participating securities and are excluded from basic shares outstanding for the year ended December 31, 2017 . The following potential common shares were excluded from the calculation of diluted net income (loss) per share attributable to common stockholders because their effect would have been anti-dilutive for the periods presented: Year Ended 2017 2016 2015 Stock options 4,902,664 10,041,403 11,806,620 Restricted stock units 435,358 2,043,544 128,200 Warrants — 33,447 182,031 Convertible preferred stock — — 16,254,123 Total anti-dilutive securities 5,338,022 12,118,394 28,370,974

Segment and Geographic Informat

Segment and Geographic Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment and Geographic Information	Note 14—Segment and Geographic Information The Company has determined it operates as one operating and reportable segment for purposes of allocating resources and evaluating financial performance. Revenue by country is based on the billing address of the seller. The following table summarizes revenue, income (loss) before income taxes and net income (loss) by geographic area (in thousands): Year Ended 2017 2016 2015 United States $ 317,755 $ 276,537 $ 213,389 International 123,476 88,430 60,110 Revenue $ 441,231 $ 364,967 $ 273,499 United States $ (44,931 ) $ 7,926 $ 11,973 International 77,196 (10,802 ) (39,967 ) Income (loss) before income taxes $ 32,265 $ (2,876 ) $ (27,994 ) United States $ 5,113 $ (18,542 ) $ (13,639 ) International 76,687 (11,359 ) (40,424 ) Net income (loss) $ 81,800 $ (29,901 ) $ (54,063 ) No individual international country’s revenue exceeded 10% of total revenue. All significant long-lived assets are located in the United States.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 15—Commitments and Contingencies Lease Commitments Capital Leases The Company entered into a credit agreement with Dell Financial Services, LLC. (“DFS”) on February 17, 2016, which provided the Company with a credit line of up to $6.0 million for hosting equipment leases (the “DFS Line”), which was increased to $9.0 million during 2017. The DFS Line allows the Company to lease hosting equipment from DFS. The leases have a 36 -month term, zero interest and are payable in equal monthly installments with a buy-out option of $1 at the end of the lease term. As of December 31, 2017 , the Company has lease obligations of approximately $4.8 million related to leased hosting equipment using the DFS Line. The Company entered into a credit agreement with ePlus Group, Inc. (“ePlus”) on January 3, 2014, which provided the Company with a credit line of up to $8.0 million for computer equipment leases (the “ePlus Line”), which was increased to $18.0 million during 2015. The ePlus Line allows the Company to order equipment from any approved vendor. ePlus purchases the equipment on behalf of the Company and leases it back to the Company. The leases have a 36 -month term, interest rate of 3.50 - 6.93% and are payable in equal monthly installments at fair market value or a $1 buy-out option at the end of the lease term depending on the equipment. As of December 31, 2017 , the Company has lease obligations of approximately $5.1 million related to leased computer equipment using the ePlus Line. The Company had a credit agreement with TriplePoint Capital, LLC (“TriplePoint”), which provided the Company with a credit line of up to $20.0 million for computer equipment leases (the “TriplePoint Line”). The TriplePoint Line allowed the Company to order equipment from any vendor. TriplePoint purchased the equipment on behalf of the Company and leased it back to the Company. The leases had a 36 -month term, interest rate of 8.25% and were payable in equal monthly installments. The Company stopped leasing equipment under the TriplePoint Line in June 2012 and paid off the remaining lease obligations during 2015 in accordance with the terms of the credit agreement. At December 31, 2017, 2016 and 2015, the Company no longer had any lease obligations related to leased computer equipment under the TriplePoint Line. For the years ended December 31, 2017, 2016 and 2015 , the accompanying Consolidated Statement of Operations includes charges of approximately $1.6 million , $1.6 million and $1.2 million for interest expense, respectively, related to the equipment leased using the DFS, ePlus and TriplePoint Lines. Operating Leases In 2015, the Company entered into a new lease for office space in London, U.K. expiring in 2025, and entered into lease extensions for existing office space in San Francisco, California and Hudson, New York expiring in 2020 and 2021, respectively. The Company did not enter into any material operating leases or extensions in 2016 or 2017. Rent expense for these operating leases is recognized over the term of each respective lease on a straight-line basis. In addition, the Company leases other office facilities under shorter terms and cancelable leases. Total rent expense for the years ended December 31, 2017, 2016 and 2015 was $4.1 million , $6.0 million and $5.1 million , respectively. Build-to-Suit Lease In May 2014, the Company entered into a 10 -year lease agreement for approximately 199,000 rentable square feet of office space in Brooklyn, New York for the Company’s new headquarters, which commenced in 2015 . Of the total new office space, approximately 172,000 rentable square feet is being accounted for as a build-to-suit lease and approximately 27,000 rentable square feet located in an adjacent building is being accounted for as an operating lease. In connection with the lease agreement, the Company established a $5.3 million collateral account, reflected in the restricted cash balance on the Consolidated Balance Sheet. Purchase Obligations The Company also has $77.3 million of non-cancelable contractual commitments as of December 31, 2017 , primarily related the initiative to migrate its data centers to the cloud, as well as other support services. These commitments are primarily due within five years. The following table represents the Company’s commitments under its current capital, operating and build-to-suit lease agreements and purchase obligations as of December 31, 2017 (in thousands): Capital Lease Operating Build-to-Suit Purchase Obligations Periods ending 2018 $ 6,697 $ 3,907 $ 9,381 $ 14,320 2019 3,556 3,912 9,451 13,332 2020 918 3,566 9,522 16,677 2021 — 2,819 10,354 16,000 2022 — 2,608 10,520 17,000 Thereafter — 8,168 38,314 — Total minimum payments required $ 11,171 $ 24,980 $ 87,542 $ 77,329 Amounts representing interest 1,258 Present value of net minimum payments 9,913 Current maturities 5,798 Long-term payment obligations $ 4,115 Non-Income Tax Contingencies The Company had reserves of $0.4 million and $0.3 million at December 31, 2017 and 2016 , respectively, for certain non-income tax obligations, representing management’s best estimate of its potential liability. The Company could also be subject to examination in various jurisdictions related to income tax and non-income tax matters. The resolution of these types of matters, if in excess of the recorded reserve, could have an adverse impact on the Company’s business. Legal Proceedings On May 13, 2015, a purported securities class action complaint ( Altayyar v. Etsy, Inc., et al. , Docket No. 1:15-cv-02785) was filed in the United States District Court for the Eastern District of New York against the Company and certain officers. The complaint was brought on behalf of a purported class consisting of all persons or entities who purchased or otherwise acquired shares of the Company's common stock from April 16, 2015 through and including May 10, 2015. It asserted violations of Sections 10(b) and 20(a) of the Securities Exchange Act of 1934 based on allegedly false or misleading statements and omissions with respect to, among other things, merchandise for sale on the Company's website that may be counterfeit or constitute trademark or copyright infringement and actions taken by third-party brands against Etsy sellers for trademark or copyright infringement. On October 22, 2015, the court appointed a lead plaintiff and lead plaintiff’s counsel. On January 21, 2016, the lead plaintiff filed an amended class action complaint alleging false or misleading statements or omissions with respect to substantially the same topics as the original complaint. The amended complaint adds certain outside directors and underwriters as defendants, expands the purported class period to be April 16, 2015 to August 4, 2015, inclusive, and asserts violations of Sections 11, 12(a)(2), and 15 of the Securities Act of 1933, as well as Sections 10(b) and 20(a) of the Securities Exchange Act of 1934. The amended complaint seeks certification as a class action and unspecified compensatory damages plus interest and attorneys' fees. On April 5, 2016, defendants moved to dismiss the amended complaint. On March 24, 2017, the court entered a judgment dismissing the amended complaint in its entirety, with prejudice, based on an opinion filed March 16, 2017. On August 2, 2017, Plaintiffs appealed to the United States Court of Appeals for the Second Circuit. The Company and the named officers and directors intend to defend themselves vigorously against this action. In light of, among other things, the early stage of the litigation, the Company is unable to predict the outcome of this matter and is unable to make a meaningful estimate of the amount or range of loss, if any, that could result from an unfavorable outcome. On July 21, 2015, a purported securities class action complaint ( Cervantes v. Dickerson, et.al ., Case No. CIV 534768) was filed in the Superior Court of State of California, County of San Mateo against the Company, certain officers, directors and underwriters. The complaint asserts violations of Sections 11 and 15 of the Securities Act of 1933. As in the Altayyar litigation, the complaint alleges misrepresentations in the Company’s Registration Statement on Form S-1 and Prospectus with respect to, among other things, merchandise for sale on the Company's website that may be counterfeit or constitute trademark or copyright infringement. The complaint seeks certification as a class action and unspecified compensatory damages plus interest and attorneys' fees. On December 7, 2015, the Company and the underwriter defendants moved to stay the Cervantes action on the grounds of forum non conveniens. On November 5, 2015, another purported securities class action complaint ( Weiss v. Etsy et al. , No. CIV 536123) was filed in the Superior Court of State of California, County of San Mateo. The Weiss complaint names as defendants the Company and the same officers, directors and underwriters named in the Cervantes complaint, and also asserts violations of Sections 11 and 15 of the Securities Act of 1933 based on allegedly false or misleading statements or omissions with respect to, among other things, merchandise for sale on the Company's website that may be counterfeit or constitute trademark or copyright infringement. On December 24, 2015, the court consolidated the Cervantes and Weiss actions. The Company and the named officers and directors intend to defend themselves vigorously against these consolidated actions. In light of, among other things, the early stage of the litigation, the Company is unable to predict the outcome of these consolidated actions and is unable to make a meaningful estimate of the amount or range of loss, if any, that could result from an unfavorable outcome. On February 3, 2016, the court granted the Company’s motion to stay the consolidated actions. In addition, from time to time in the normal course of business, various other claims and litigation have been asserted or commenced against the Company. Due to uncertainties inherent in litigation and other claims, the Company can give no assurance that it will prevail in any such matters, which could subject the Company to significant liability for damages. Any claims or litigation, regardless of their success, could have an adverse effect on the Company’s consolidated results of operations or cash flows in the period the claims or litigation are resolved. Although the results of litigation and claims cannot be predicted with certainty, we currently believe that the final outcome of these ordinary course matters will not have a material adverse effect on our business.

Basis of Presentation and Sum23

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Consolidation	Basis of Consolidation The consolidated financial statements include the accounts of Etsy and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with accounting principles generally accepted in the United States of America (“GAAP”) requires management to make estimates and judgments 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. The accounting estimates that require management’s most difficult and subjective judgments include revenue recognition, income taxes, website development costs and internal-use software, purchase price allocations for business combinations, valuation of goodwill and intangible assets, leases, stock-based compensation and restructuring and other exit costs. The Company evaluates its estimates and judgments on an ongoing basis and revises them when necessary. Actual results may differ from the original or revised estimates.
Revenue Recognition	Revenue Recognition The Company's revenue is diversified, generated from a mix of marketplace activities and the services and tools provided to Etsy sellers to help them start, manage, and scale their business. The Company recognizes revenue when all of the following conditions are satisfied: (1) there is persuasive evidence of an arrangement; (2) the service has been provided to the Etsy seller; (3) the collection of fees is reasonably assured; and (4) the amount of fees to be paid by the Etsy seller is fixed or determinable. The Company evaluates whether it is appropriate to recognize revenue on a gross or net basis based upon its evaluation of whether it is the primary obligor in a transaction, has inventory risk and has latitude in establishing pricing and selecting suppliers, among other factors. Marketplace revenue . Marketplace revenue is primarily comprised of the 3.5% transaction fee that an Etsy seller pays for each completed transaction, exclusive of shipping fees charged, and the listing fee of $0.20 she pays for each item she lists on Etsy.com. Transaction fees are recognized when the corresponding transaction is made. Listing fees are recognized ratably over a four -month listing period, unless the item is sold or the seller relists it, at which time any remaining listing fee is recognized. Seller Services revenue . Seller Services revenue consists of fees an Etsy seller pays for the Company's four paid services: Etsy Payments (formerly called Direct Checkout), Promoted Listings, Shipping Labels and Pattern. • Revenue from Etsy Payments consists of fees an Etsy seller pays the Company to process credit, debit and Etsy Gift Card payments. Etsy Payments fees vary between 3 - 4% of the item’s total sale price plus a flat fee per order, depending on the country in which her bank account is located. Etsy Payments fees are based on the item’s total sale price, including shipping. Revenue from Etsy Payments is recognized when the corresponding transaction is consummated. • Revenue from Promoted Listings consists of cost-per-click fees an Etsy seller pays for prominent placement of her listings in search results generated by Etsy buyers in the Company's marketplace. Revenue is recognized when the Promoted Listing is clicked. • Revenue from Shipping Labels consists of fees an Etsy seller pays the Company when she purchases shipping labels through its platform, net of the cost the Company incurs in purchasing those shipping labels. The Company provides its sellers shipping labels from the United States Postal Service, FedEx and Canada Post at discounted pricing due to the volume of purchases through its platform. The Company recognizes Shipping Label revenue when an Etsy seller purchases a shipping label. The Company recognizes Shipping Label revenue on a net basis as it is not the primary obligor in the delivery of these services. • Revenue from Pattern consists of monthly subscription and annual domain registration fees an Etsy seller pays to use the Company's custom website services. The Company recognizes revenue from Pattern ratably over the term of the subscription. Other revenue . Other revenue includes the fees the Company receives from commercial partnerships, which are recognized as earned in accordance with the Company's revenue recognition policy.
Cost of Revenue	Cost of Revenue Cost of revenue primarily consists of the cost of interchange and other fees for credit card processing services, credit card verification service fees and credit card chargebacks to support Etsy Payments revenue and costs of refunds made to Etsy buyers that the Company is not able to collect from Etsy sellers. Cost of revenue also includes expenses associated with the operation and maintenance of the Company’s platform and data centers, including depreciation and amortization, employee-related costs and hosting and bandwidth costs.
Accounts Receivable and Allowance for Doubtful Accounts	Accounts Receivable and Allowance for Doubtful Accounts The Company’s trade accounts receivable are recorded at amounts billed to Etsy sellers and are presented on the Consolidated Balance Sheet net of the allowance for doubtful accounts. The allowance is determined by a number of factors, including age of the receivable, current economic conditions, historical losses and management’s assessment of the financial condition of Etsy sellers. Receivables are written off once they are deemed uncollectible, which may arise when Etsy sellers file for bankruptcy or are otherwise deemed unable to repay the amounts owed to the Company. Estimates of uncollectible accounts receivable are recorded to general and administrative expense.
Funds Receivable and Seller Accounts and Funds Payable and Amounts Due to Sellers	Funds Receivable and Seller Accounts and Funds Payable and Amounts due to Sellers The Company records funds receivable and seller accounts and funds payable and amounts due to sellers as current assets and liabilities, respectively, on the Consolidated Balance Sheet. Funds receivable and seller accounts represent amounts received or expected to be received from Etsy buyers via third-party credit card processors, which flow through an Etsy bank account for payment to Etsy sellers. This cash and related receivable represent the total amount due to sellers, and as such a liability for the same amount is recorded to funds payable and amounts due to Etsy sellers.
Property and Equipment	Property and Equipment Property and equipment, consisting principally of building, computer equipment and leasehold improvements, are recorded at cost. The Company capitalizes construction in progress for build-to-suit lease agreements where we are the owner, for accounting purposes only, during the construction period. Depreciation and amortization begin at the time the asset is placed into service and are recognized using the straight-line method in amounts sufficient to relate the cost of depreciable and amortizable assets to operations over their estimated useful lives. Repairs and maintenance are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation or amortization are removed from the balance sheet and the resulting gain or loss is reflected in operations. When events or changes in circumstances require, the Company assesses the likelihood of recovering the cost of tangible long-lived assets based on its expectations of future profitability, undiscounted cash flows and management’s plans with respect to operations to determine if the asset is impaired and subject to write-off. Measurement of any impairment loss is based on the excess of the carrying value of the asset over the fair value.
Website Development and Internal-use Software Costs	Website Development and Internal-use Software Costs Costs incurred to develop the Company's website and software for internal-use are capitalized and amortized over the estimated useful life of the software, generally three years. In accordance with authoritative accounting guidance, capitalization of costs to develop software begin when preliminary development efforts are successfully completed, management has authorized and committed project funding and it is probable that the project will be completed and the software will be used as intended. The Company also capitalizes costs related to upgrades and enhancements when it is probable the expenditures will result in additional functionality or will extend the useful life of existing functionality. Costs related to the design or maintenance of website development and internal-use software are expensed as incurred. The Company periodically reviews website development and internal-use software costs to determine whether the projects will be completed, placed in service, removed from service or replaced by other internally developed or third-party software. If the asset is not expected to provide any future use, the asset is retired and any unamortized cost is expensed. If an asset will continue to be used, but the net book value is not expected to be fully recoverable, the asset is impaired to its fair value. When events or changes in circumstances require, the Company assesses the likelihood of recovering the cost of website development and internal-use software costs based on its expectations of future profitability, undiscounted cash flows and our plans with respect to operations to determine if the asset is impaired and subject to write-off. Measurement of any impairment loss is based on the excess of the carrying value of the asset over the fair value. If a cloud computing arrangement includes a software license, then the Company accounts for the software license element of the arrangement consistent with the acquisition of other software licenses. If a cloud computing arrangement does not include a software license, the Company accounts for the arrangement as a service contract. Capitalized website development and internal-use software costs are included in property and equipment within the Consolidated Balance Sheets.
Leases	Leases The Company leases office space and certain computer equipment in multiple locations under non-cancelable lease agreements. The leases are reviewed for classification as operating, capital or build-to-suit leases. For operating leases, rent is recognized on a straight-line basis over the lease period. For capital leases, the Company records the leased asset with a corresponding liability. Payments are recorded as reductions to the liability with an appropriate interest charge recorded based on the then-outstanding remaining liability. The Company considers the nature of the renovations and the Company’s involvement during the construction period of newly leased office space to determine if it is considered, for accounting purposes only, to be the owner of the construction project during the construction period. If the Company determines that it is the owner of the construction project, it is required to capitalize the fair value of the building as well as the construction costs incurred on its Consolidated Balance Sheet along with a corresponding financing liability (“build-to-suit accounting”). Upon occupancy for build-to-suit leases, the Company assesses whether the circumstances qualify for sales recognition under the sale-leaseback accounting guidance. If the lease meets the sale-leaseback criteria, the Company will remove the asset and related financial obligation from the balance sheet and treat the building lease as an operating lease. If upon completion of construction, the project does not meet the sale-leaseback criteria, the leased property will be treated as a capital lease for financial reporting purposes. In May 2016, the Company took possession of its corporate headquarters in Brooklyn, New York upon substantial completion of the construction phase of the build-out. Upon completion of the project, the Company performed a sale-leaseback analysis pursuant to Accounting Standards Codification (“ASC”) 840 —Leases , to determine the appropriateness of removing the previously capitalized assets from the Consolidated Balance Sheets. The Company concluded that components of “continuing involvement” were evident as a result of this review, precluding the derecognition of the related assets from the Consolidated Balance Sheets. In conjunction with the initiation of the lease in May 2014, the Company also recorded a facility financing obligation equal to the fair market value of the assets received from the landlord. As of December 31, 2017 , the facility financing obligation outstanding was $60.0 million . At the end of the lease term, including exercise of any renewal options, the remaining value of the net facility financing obligation over the net carrying value of the fixed asset will be recognized as a non-cash gain on sale of the property. The Company does not report rent expense for the lease. Rather, rental payments under the lease are recognized as a reduction of the financing obligation and interest expense, and the associated asset capitalized throughout the construction project is depreciated over its estimated useful life.
Income Taxes	Income Taxes The income tax benefit (provision) is based on income (loss) before income taxes and is accounted for under the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to settle. The effect on deferred tax assets and liabilities of a change in tax rates is recognized as income or expense in the period that includes the enactment date. Management assesses the need for a valuation allowance on a quarterly basis to reduce deferred tax assets to the amounts expected to be realized. The Company accounts for uncertainty in income taxes using a recognition threshold and a measurement attribute for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by the taxing authorities. The amount recognized is measured as the largest amount of benefit that has a greater than 50% likelihood of being realized upon ultimate audit settlement. The Company recognizes interest and penalties, if any, associated with income tax matters as part of the income tax provision and includes accrued interest and penalties with the related income tax liability in the Consolidated Balance Sheet.
Business Combinations	Business Combinations The Company has completed a number of acquisitions of other businesses in the past and may acquire additional businesses or technologies in the future. The results of businesses acquired in a business combination are included in the Company’s consolidated financial statements from the date of acquisition. The Company allocates the purchase price, which is the sum of the consideration provided and may consist of cash, equity or a combination of the two, in a business combination to the identifiable assets and liabilities of the acquired business at their acquisition date fair values. The excess of the purchase price over the amount allocated to the identifiable assets and liabilities, if any, is recorded as goodwill. Determining the fair value of assets acquired and liabilities assumed requires management to use significant judgment and estimates, including the selection of valuation methodologies, estimates of future revenue and cash flows, discount rates and selection of comparable companies. When the Company issues stock-based or cash awards to an acquired company’s stockholders, the Company evaluates whether the awards are contingent consideration or compensation for post-combination services. The evaluation includes, among other things, whether the vesting of the awards is contingent on the continued employment of the acquired company’s stockholder beyond the acquisition date. If continued employment is required for vesting, the awards are treated as compensation for post-combination services and recognized as expense over the requisite service period. The Company initially recognizes intangible assets at fair value, and amortizes them on a straight-line basis over their estimated useful lives. When circumstances indicate that the carrying value of these assets may not be recoverable, the Company reviews its identifiable amortizable intangible assets for impairment. To date, the assets acquired and liabilities assumed in the Company’s business combinations have primarily consisted of goodwill and finite-lived intangible assets, consisting primarily of developed technologies, customer relationships and trademarks. The estimated fair values and useful lives of identifiable intangible assets are based on many factors, including estimates and assumptions of future operating performance and cash flows of the acquired business, the nature of the business acquired and the specific characteristics of the identified intangible assets. The estimates and assumptions used to determine the fair values and useful lives of identified intangible assets could change due to numerous factors, including market conditions, technological developments, economic conditions and competition. In connection with determination of fair values, the Company may engage independent appraisal firms to assist with the valuation of intangible and certain tangible assets acquired and certain assumed obligations. Acquisition-related transaction costs incurred by the Company are not included as a component of consideration transferred, but are accounted for as an expense in the period in which the costs are incurred.
Goodwill	Goodwill Goodwill represents the excess of the aggregate fair value of the consideration transferred in a business combination over the fair value of the assets acquired, net of liabilities assumed. Goodwill is not amortized, but is subject to an annual impairment test. Management has determined that the Company has a single reporting unit and performs its annual goodwill impairment test during the fourth quarter or more frequently if events or changes in circumstances indicate that the goodwill may be impaired. Events or changes in circumstances which could trigger an impairment review include significant changes in the manner of the Company’s use of the acquired assets or the strategy for the Company’s overall business, significant negative industry or economic trends, significant underperformance relative to historical or projected future results of operations, a significant adverse change in the business climate, cost factors that have a negative effect on earnings and cash flows, an adverse action or assessment by a regulator, a sustained decrease in share price, unanticipated competition or a loss of key personnel. The Company has the option to first assess qualitative factors to determine whether the existence of events or circumstances leads to a determination that it is more likely than not that the fair value of the reporting unit is less than its carrying amount. If, after assessing the totality of events or circumstances, the Company determines it is not more likely than not that the fair value of the reporting unit is less than its carrying amount, then additional impairment testing is not required. However, if the Company concludes otherwise, then it is required to perform a quantitative assessment for impairment. The quantitative assessment involves comparing the estimated fair value of the reporting unit with its respective book value, including goodwill. If the estimated fair value exceeds book value, goodwill is considered not to be impaired and no additional steps are necessary. If, however, the book value of the reporting unit exceeds the fair value, an impairment loss is recognized in an amount equal to the excess, not to exceed the total amount of goodwill allocated to that reporting unit.
Intangible Assets	Intangible Assets Intangible assets are amortized over the estimated useful life of the acquired technology, customer relationships and trademarks, generally three years. When events or changes in circumstances require, the Company assesses the likelihood of recovering the cost of intangible assets based on its expectations of future profitability, undiscounted cash flows and management’s plans with respect to operations to determine if the asset is impaired and subject to write-off. Measurement of any impairment loss is based on the excess of the carrying value of the asset over the fair value.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). Stock options and restricted stock units (“RSUs”) are awarded to employees and members of our Board of Directors and are measured at fair value at each grant date. The Company calculates the fair value of stock options on the date of grant using the Black-Scholes option-pricing model and the expense is recognized over the requisite service period for awards expected to vest. Prior to the IPO, the Company utilized equity valuations based on comparable publicly-traded companies, discounted free cash flows, an analysis of the Company's enterprise value and other factors deemed relevant in estimating the fair value of its common stock. Subsequent to the IPO, the Company has used the closing price of its common stock on Nasdaq as the fair value of its common stock. The risk-free rate for periods within the contractual life of the option is based on the U.S. Treasury yield curve in effect at the time of grant. Expected volatilities are based on implied volatilities from market comparisons of certain publicly traded companies and other factors. The expected term of stock options granted has been determined using the simplified method, which uses the midpoint between the vesting date and the contractual term. The fair value of RSUs is determined based on the closing price of the Company's common stock on Nasdaq on the grant date. The requisite service period for stock options and RSUs is generally four years from the date of grant. In the first quarter of 2017, the Company made an accounting policy election to recognize forfeitures as they occur upon adoption of guidance in ASU 2016-09, Compensation—Stock Compensation: Scope of Modification Accounting . In reporting periods prior to 2017, the Company estimated forfeitures at the time of grant and revised in subsequent periods as necessary if actual forfeitures differed from estimates. The Company accounts for stock-based compensation arrangements related to the ALM acquisition in restricted shares subject to a put option that allows the holder of the shares to put the shares back to the Company for cash as liability-classified stock awards. These awards are re-measured at fair value each reporting period, with changes in fair value being charged to the statement of operations. Compensation expense is recognized using a graded vesting methodology for each separately vesting tranche as though the award were, in substance, multiple awards. Unless the put option is exercised, the restricted shares will be reclassified from a liability to an equity classified award upon the termination of the put option at the vesting of each separate tranche.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all investments with an original maturity of three months or less at time of purchase to be cash equivalents. Cash restricted by third parties is not considered cash and cash equivalents.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist of cash and cash equivalents, short-term investments and funds receivable and seller accounts. The Company reduces credit risk by placing its cash and cash equivalents with major financial institutions with high credit ratings. At times, such amounts may exceed federally insured limits.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Management believes that the fair value of financial instruments, consisting of cash and cash equivalents, short-term investments, accounts receivable, funds receivable and seller accounts, accounts payable and funds payable and seller accounts, approximates carrying value due to the immediate or short-term maturity associated with these instruments.
Marketing	Marketing Marketing expenses largely consist of direct marketing and indirect employee-related expenses to support our marketing initiatives. Direct marketing includes digital marketing, brand marketing, seller lifecycle and growth activities, public relations and communications and marketing partnerships. Digital marketing primarily consists of targeted promotional campaigns through electronic channels, such as product listing ads, search engine marketing, affiliate programs and display advertising which are focused on buyer acquisition and brand marketing.
Product Development	Product development Product development expenses consist primarily of employee-related expenses for engineering, product management, product design and product research activities. Additional expenses include consulting costs related to the development, quality assurance and testing of new technology and enhancement of our existing technology.
Net Income (Loss) Per Share	Net Income (Loss) Per Share The Company follows the two-class method when computing net income (loss) per share as the Company has issued restricted shares that meet the definition of participating securities in connection with the acquisition of Blackbird Technologies, Inc (“Blackbird”) in 2016. The two-class method determines net income (loss) per share for each class of common stock and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common stock and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. The Company will continue to implement the two-class method when computing net income (loss) per share through the end of the three year vesting term for these restricted shares. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding for the period. Diluted net income (loss) per share is computed by dividing net income (loss) for the period by the weighted average number of shares of common stock and potentially dilutive common stock outstanding during the period. The dilutive effect of outstanding options and stock-based compensation awards is reflected in diluted net income (loss) per share by application of the treasury stock method. The calculation of diluted net income (loss) per share excludes all anti-dilutive common shares. For periods in which the Company has reported net losses, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, because dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.
Contingencies	Contingencies The Company accrues for loss contingencies when losses become probable and are reasonably estimable. If the reasonable estimate of the loss is a range and no amount within the range is a better estimate, the minimum amount of the range is recorded as a liability. The Company does not accrue for contingent losses that, in its judgment, are considered to be reasonably possible, but not probable; however, it discloses the range of such reasonably possible losses.
Segment Data	Segment Data The Company identifies operating segments as components of an entity for which discrete financial information is available and is regularly reviewed by the chief operating decision maker, or decision-making group, in making decisions regarding resource allocation and performance assessment. The Company defines the term “chief operating decision maker” to be its chief executive officer. The Company has determined it operates in one operating segment and one reportable segment, as its chief operating decision maker reviews financial information presented on only a consolidated basis for purposes of allocating resources and evaluating financial performance.
Foreign Currency	Foreign Currency The Company has determined that the functional currency for each of its foreign operations is the currency of the primary cash flow of the operations, which is generally the local currency in which the operation is located. All assets and liabilities are translated into U.S. dollars using exchange rates in effect at the balance sheet date. Revenue and expenses are translated using average exchange rates during the period. Foreign currency translation adjustments are reflected in stockholders’ equity as a component of other comprehensive income (loss). Transaction gains and losses including intercompany balances denominated in a currency other than the functional currency of the entity involved are included in foreign exchange gain (loss) within other income (expense) in the Consolidated Statement of Operations.
Excess Tax Benefits from Exercise of Stock Options	Excess Tax Benefits from Exercise of Stock Options As of the first quarter of 2017, the Company adopted ASU 2016-09, Stock Compensation: Improvements to Employee Share-based Payment Accounting , for share-based payment transactions that require a reporting entity to recognize excess tax benefits and deficiencies as income tax expense or benefit in the income statement. Prior to this adoption, including years ended December 31, 2015 and December 31, 2016, the Company used the “with and without” approach in determining the order in which tax attributes were utilized. As a result, the Company recognized a tax benefit from stock-based awards (“windfall”) in additional paid-in capital only if an incremental tax benefit was realized after all other tax attributes available to the Company had been utilized. When tax deductions from stock-based awards were less than the cumulative book compensation expense, the tax effect of the resulting difference (“shortfall”) was charged first to additional paid-in capital, to the extent of the Company’s pool of windfall tax benefits, with any remainder recognized in income tax expense.
Recent Accounting Pronouncements	Recently Issued Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued ASU 2014-09, Revenue from Contracts with Customers , and additional changes, modifications, clarifications or interpretations related to this guidance thereafter, which replaces existing revenue recognition guidance. The new guidance is effective for the annual and interim periods beginning after December 15, 2017. Among other things, the updated guidance requires companies to recognize revenue in a way that depicts the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 provides companies with two implementation methods. Companies can choose to apply the standard retrospectively to each prior reporting period presented (full retrospective application) or retrospectively with the cumulative effect of initially applying the standard as an adjustment to the opening balance of retained earnings of the annual reporting period that includes the date of initial application (modified retrospective application). The Company will adopt this new standard effective January 1, 2018 using the full retrospective approach. The Company has performed an assessment of its revenue streams and does not expect the adoption of this standard to result in changes to the Company's revenue recognition and therefore the impact will be limited to additional disclosures as required by the new guidance. The Company is currently performing an assessment over data availability and the presentation that will be necessary to meet additional disclosure requirements. In February 2016, the FASB issued ASU 2016-02, Leases , which requires a reporting entity to recognize right-of-use assets and lease liabilities on the balance sheet for operating leases to increase transparency and comparability. The new guidance is effective for annual and interim periods beginning after December 15, 2018, and early adoption is permitted. Upon adoption of this standard, the Company expects to recognize, on a discounted basis, its minimum commitments under noncancelable operating leases on the Consolidated Balance Sheets resulting in the recording of right of use assets and lease obligations. The Company is currently evaluating whether there are any additional impacts this guidance will have on its consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments , which requires credit losses on financial assets measured at amortized cost basis to be presented at the net amount expected to be collected, not based on incurred losses. Further, credit losses on available-for-sale debt securities should be recorded through an allowance for credit losses limited to the amount by which fair value is below amortized cost. The new standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018 is permitted. We are evaluating the impact of adopting this new accounting guidance on our consolidated financial statements. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows: Restricted Cash , which requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents and amounts generally described as restricted cash or restricted cash equivalents. The new guidance is effective for the annual and interim periods beginning after December 15, 2017 and early adoption is permitted. The Company is currently evaluating the effect this guidance will have on its consolidated financial statements, but does not expect it to have a significant impact on its consolidated financial statements because its balance of restricted cash does not change significantly from period to period. Recently Adopted Accounting Pronouncements In March 2016, the FASB issued ASU 2016-09, Stock Compensation: Improvements to Employee Share-based Payment Accounting , that requires a reporting entity to recognize excess tax benefits and deficiencies as income tax expense or benefit in the income statement, and simplifies other aspects of accounting and presentation requirements for share-based payment transactions. The new guidance is effective for annual and interim periods beginning after December 15, 2016, and early adoption is permitted for financial statements as of the beginning of an interim or annual reporting period. The Company adopted this standard in the first quarter of 2017. As a result of this updated guidance, the Company recorded $12.8 million of excess tax benefits, rather than additional paid-in capital, for the year ended December 31, 2017. On a prospective basis after adoption, the Company has updated its calculation of diluted earnings per share to exclude excess tax benefits previously included in the calculation of assumed proceeds under the treasury stock method. The Company has elected to apply the updated guidance on cash flow classification of excess tax benefits as operating activities using a retrospective approach for consistent year-over-year comparability. The Company has elected to recognize forfeitures as they occur on a modified retrospective basis and to adopt the amendments on statutory withholding requirements on a prospective basis, both of which have no material impact to the consolidated financial statements. In October 2016, the FASB issued ASU 2016-16, Income Taxes: Intra-entity Transfers of Assets other than Inventory , which eliminated the exception that previously existed for the income tax consequences of intra-entity asset transfers other than inventory. The new guidance is effective for annual and interim periods beginning after December 15, 2017. Early adoption is permitted in annual reporting periods for which interim or annual financial statements have not been issued. The Company adopted this standard in the first quarter of 2017. The amendments in this update have been applied on a modified retrospective basis through a cumulative effect adjustment recorded to accumulated deficit as of January 1, 2017 of $51.4 million , which represents the unamortized amount of the deferred tax charge asset on the balance sheet at December 31, 2016. Consequently, the adoption of this standard eliminates the recognition in the tax provision of $17.1 million in each year through 2019, the year through which the deferred tax charge was previously amortizable. Additionally, a deferred tax asset of $21.7 million was recognized which previously qualified for an exception that has been eliminated. A full valuation allowance for that deferred tax asset was also recognized resulting in no impact to the consolidated financial statements. In January 2017, the FASB issued ASU 2017-01, Business Combinations: Clarifying the Definition of a Business , to clarify the definition of a business and provide guidance for evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The new guidance is to be applied on a prospective basis and is effective for the annual and interim periods beginning after December 15, 2017. The Company adopted this standard in the fourth quarter of 2017 noting no material impact to the consolidated financial statements. In January 2017, the FASB issued ASU 2017-04, Intangibles—Goodwill and Other: Simplifying the Test for Goodwill Impairmen t, to simplify the measurement of goodwill impairment by eliminating step two from the goodwill impairment test. The new guidance requires goodwill impairment to be measured as the amount by which a reporting unit’s carrying value exceeds its fair value, not to exceed the total amount of goodwill allocated to that reporting unit. The new guidance is effective for the annual and interim periods beginning after December 15, 2019 and early adoption is permitted. The Company adopted this standard in the fourth quarter of 2017 noting no material impact to the consolidated financial statements. In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation: Scope of Modification Accounting , to increase comparability and provide clarity on whether changes in the terms or conditions in a share-based payment award require a reporting entity to apply modification guidance per FASB Accounting Standards Codification Topic 718. The new guidance is to be applied on a prospective basis, is effective for the annual and interim periods beginning after December 15, 2017 and early adoption is permitted. The Company adopted this standard in the fourth quarter of 2017 noting no material impact to the consolidated financial statements.

Basis of Presentation and Sum24

Basis of Presentation and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Revenue by Type of Service	The following table summarizes revenue by type of service (in thousands): Year Ended 2017 2016 2015 Marketplace $ 179,492 $ 158,204 $ 132,648 Seller Services 258,453 200,857 136,608 Other 3,286 5,906 4,243 Revenue $ 441,231 $ 364,967 $ 273,499
Schedule of Allowance Activity	The following table summarizes the allowance activity during the periods indicated (in thousands): Year Ended 2017 2016 2015 Balance as of the beginning of period $ 1,999 $ 2,071 $ 1,841 Bad debt expense 2,497 1,770 1,780 Write-offs, net of recoveries and other adjustments (1,809 ) (1,842 ) (1,550 ) Balance as of the end of period $ 2,687 $ 1,999 $ 2,071

Business Combinations (Tables)

Business Combinations (Tables)	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The below table summarizes the components of the Blackbird purchase price and allocation of the purchase price at fair value (in thousands): Cash paid $ 8,050 Common shares 6,966 Total purchase consideration $ 15,016 Net working capital $ 81 Developed technology 7,200 Customer relationships 1,250 Goodwill 8,660 Deferred tax liability (2,175 ) Net assets acquired $ 15,016
Summary of Unaudited Pro Forma Financial Information	The unaudited pro forma financial information is presented in the table below for the years ended December 31, 2016 and 2015 (in thousands except per share amounts): Year Ended December 31, 2016 2015 Revenue $ 365,786 $ 273,616 Net loss (35,401 ) (65,106 ) Basic and diluted net loss per share (0.31 ) (0.71 )

Restructuring and Other Exit 26

Restructuring and Other Exit Costs (Tables)	12 Months Ended
	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Schedule of Restructuring Reserve by Type of Cost	The following table displays restructuring and other exit costs recorded related to the Actions and a rollforward of the charges to the accrued balance as of December 31, 2017 (in thousands): Severance Charge Stock-Based Compensation Other Exit Costs Total Balance, December 31, 2016 $ — $ — $ — $ — Total restructuring and other exit costs 8,972 1,668 620 11,260 Costs charged against equity/assets — (1,668 ) — (1,668 ) Cash payments (2,110 ) — (278 ) (2,388 ) Balance, June 30, 2017 6,862 — 342 7,204 Total restructuring and other exit costs 871 965 (70 ) 1,766 Costs charged against equity/assets — (965 ) — (965 ) Cash payments (4,385 ) — (180 ) (4,565 ) Balance, September 30, 2017 3,348 — 92 3,440 Total restructuring and other exit costs 361 68 442 871 Costs charged against equity/assets — (68 ) (286 ) (354 ) Cash payments (2,401 ) — (214 ) (2,615 ) Balance, December 31, 2017 $ 1,308 $ — $ 34 $ 1,342
Restructuring and Related Costs	Total restructuring and other exit costs included in the Consolidated Statements of Operations are as follows (in thousands): Year Ended 2017 2016 2015 Cost of revenue $ 738 $ — $ — Marketing 2,950 — — Product development 3,232 — — General and administrative 6,977 — — Total restructuring and other exit costs $ 13,897 $ — $ —

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements, Recurring	The following are the major categories of assets and liabilities measured at fair value on a recurring basis as of the dates indicated (in thousands): As of December 31, 2017 Level 1 Level 2 Level 3 Total Asset Cash equivalents: Commercial paper $ — $ 11,290 $ — $ 11,290 Money market funds 204,867 — — 204,867 U.S. Government and agency securities 24,989 — — 24,989 229,856 11,290 — 241,146 Short-term investments: Commercial paper — 2,998 — 2,998 Corporate bonds — 12,748 — 12,748 U.S. Government and agency securities 9,362 — — 9,362 9,362 15,746 — 25,108 Funds receivable and seller accounts: Money market funds 14,144 — — 14,144 14,144 — — 14,144 $ 253,362 $ 27,036 $ — $ 280,398 As of December 31, 2016 Level 1 Level 2 Level 3 Total Asset Cash equivalents: Commercial paper $ — $ 2,997 $ — $ 2,997 Money market funds 98,161 — — 98,161 U.S. Government and agency securities 1,950 — — 1,950 100,111 2,997 — 103,108 Short-term investments: Commercial paper — 17,146 — 17,146 Corporate bonds — 33,303 — 33,303 U.S. Government and agency securities 50,045 — — 50,045 50,045 50,449 — 100,494 $ 150,156 $ 53,446 $ — $ 203,602 Liability Post-combination compensation classified as liability $ — $ — $ 2,067 $ 2,067 $ — $ — $ 2,067 $ 2,067
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation	The table below provides a reconciliation of the beginning and ending balances for the liabilities measured at fair value using significant unobservable inputs (Level 3) (in thousands): Year Ended 2017 2016 Balance at beginning of period $ 2,067 $ 2,357 Changes to liability-classified stock awards 771 1,652 Conversion of liability-classified instruments to equity (2,838 ) (1,942 ) Balance at end of period $ — $ 2,067

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Summary of Cost and Fair Value of Available-For-Sale Securities	The cost and fair value of available-for-sale securities were as follows as of the dates indicated (in thousands): Cost Gross Gross Fair Value December 31, 2017 Cash equivalents: Commercial paper $ 11,290 $ — $ — $ 11,290 U.S. Government and agency securities 24,990 (1 ) — 24,989 36,280 (1 ) — 36,279 Short-term investments: Commercial paper 2,998 — — 2,998 Corporate bonds 12,754 (6 ) — 12,748 U.S. Government and agency securities 9,352 (1 ) 11 9,362 25,104 (7 ) 11 25,108 $ 61,384 $ (8 ) $ 11 $ 61,387 December 31, 2016 Cash equivalents: Commercial paper $ 2,997 $ — $ — $ 2,997 2,997 — — 2,997 Short-term investments: Commercial paper 17,146 — — 17,146 Corporate bonds 33,318 (16 ) 1 33,303 U.S. Government and agency securities 50,059 (15 ) 1 50,045 100,523 (31 ) 2 100,494 $ 103,520 $ (31 ) $ 2 $ 103,491

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consisted of the following as of the dates indicated (in thousands): As of Estimated useful lives 2017 2016 Computer equipment 3 years $ 35,587 $ 30,378 Furniture and equipment 2 - 4 years 6,194 5,920 Software 1 - 3 years 908 856 Leasehold improvements Shorter of life of asset or lease term 10,929 10,155 Building 25 years 81,892 81,957 Website development 3 years 48,333 43,294 183,843 172,560 Less: Accumulated depreciation and amortization 66,226 46,153 $ 117,617 $ 126,407
Summary of Capitalized Website Development and Internal-Use Software Activities	The following table summarizes capitalized website development and internal-use software activities during the periods indicated (in thousands): Year Ended 2017 2016 Balance as of the beginning of the period $ 43,294 $ 33,469 Additions to website development, excluding stock-based compensation 10,028 11,769 Additions to website development—stock-based compensation 807 792 Less: Retirements 625 2,736 Less: Impairments 5,171 — 48,333 43,294 Less: Accumulated amortization balance as of the beginning of the period 24,155 19,676 Amortization Expense 8,209 6,333 Less: Retirements 364 1,854 Less: Impairments 2,009 — Accumulated amortization balance as of the end of the period 29,991 24,155 $ 18,342 $ 19,139

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The following table summarizes the changes in the carrying amount of goodwill for the periods indicated (in thousands): Year Ended 2017 2016 Balance as of the beginning of the period $ 35,657 $ 27,752 Acquisitions(1) — 8,660 Foreign currency translation adjustments 2,884 (755 ) Balance as of the end of the period $ 38,541 $ 35,657 (1) Includes goodwill as a result of the Blackbird Technologies acquisition. See “ Note 2—Business Combinations ” for more information.
Schedule of Finite-Lived Intangible Assets	At December 31, 2017 and 2016 , the gross book value and accumulated amortization of intangible assets were as follows (in thousands): As of December 31, 2017 As of December 31, 2016 Gross book Accumulated Net book Gross book Accumulated Net book Technology $ 7,200 $ (3,100 ) $ 4,100 $ 10,466 $ (3,536 ) $ 6,930 Customer relationships — — — 1,250 (673 ) 577 Intangible assets, net $ 7,200 $ (3,100 ) $ 4,100 $ 11,716 $ (4,209 ) $ 7,507 (1) Excludes the gross book value and accumulated amortization of fully amortized intangibles.
Schedule of Future Amortization Expense	Based on amounts recorded at December 31, 2017 , the Company estimates intangible asset amortization expense in each of the years ending December 31 as follows (in thousands): 2018 $ 2,400 2019 1,700 Thereafter — Total amortization expense $ 4,100

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Class of Treasury Stock	The following table summarizes the Company's share repurchase activity, excluding shares withheld to satisfy tax withholding obligations in connection with the vesting of employee restricted stock units (in thousands except share and per share amounts): Shares Repurchased Average Price Paid per Share (1) Value of Shares Repurchased Remaining Amount Authorized Balance as of November 17, 2017 — $ — $ — $ 100,000 Repurchases of common stock for the three months ended: December 31, 2017 586,231 17.57 10,301 (10,301 ) Balance as of December 31, 2017 586,231 $ 17.57 $ 10,301 $ 89,699 (1) Average price paid per share excludes broker commissions.

Stock-based Compensation (Table

Stock-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	The fair value of options granted in each year using the Black-Scholes pricing model has been based on the following assumptions: Year Ended 2017 2016 2015 Volatility 41.7% - 44.2% 38.6% - 44.6% 40.4% - 45.0% Risk-free interest rate 1.9% - 2.2% 1.1% - 2.1% 1.3% - 1.9% Expected term (in years) 5.5 - 6.3 5.5 - 6.3 5.5 - 6.1 Dividend rate —% —% —%
Schedule of Share-based Compensation, Stock Options, Activity	The following table summarizes the activity for the Company’s options (in thousands except share and per share amounts): Shares Weighted-Average Weighted-Average Aggregate Outstanding at December 31, 2014 11,525,279 $ 5.34 7.57 $ 134,386 Granted 1,660,170 16.19 Exercised (1,315,735 ) 2.76 Forfeited/Canceled (800,855 ) 9.94 Outstanding at December 31, 2015 11,068,859 6.94 7.01 31,932 Granted 1,700,234 9.35 Exercised (2,535,620 ) 4.17 Forfeited/Canceled (893,906 ) 9.51 Outstanding at December 31, 2016 9,339,567 7.89 6.64 43,613 Granted 5,887,183 11.04 Exercised (5,760,263 ) 5.87 Forfeited/Canceled (1,518,548 ) 11.36 Outstanding at December 31, 2017 7,947,939 11.02 7.93 74,996 Total exercisable at December 31, 2017 2,294,818 10.48 4.81 22,912
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	The following table summarizes the weighted average grant date fair value of options granted, intrinsic value of options exercised and fair value of awards vested in periods indicated (in thousands except per share amounts): Year Ended December 31, 2017 2016 2015 Weighted average grant date fair value of options granted $ 4.85 $ 4.03 $ 6.89 Intrinsic value of options exercised 52,693 19,130 15,148 Fair value of awards vested 19,826 9,533 8,337
Summary of the Activity of Unvested RSUs	The following table summarizes the activity for the Company’s unvested RSUs: Shares Weighted-Average Unvested at December 31, 2014 — $ — Granted 407,368 13.78 Vested — — Forfeited/Canceled (11,522 ) 16.76 Unvested at December 31, 2015 395,846 13.70 Granted 3,200,297 10.29 Vested (255,868 ) 10.64 Forfeited/Canceled (205,094 ) 10.15 Unvested at December 31, 2016 3,135,181 10.70 Granted 2,360,315 12.17 Vested (1,072,321 ) 10.44 Forfeited/Canceled (1,348,928 ) 10.56 Unvested at December 31, 2017 3,074,247 11.98
Schedule of Share-based Compensation, Allocation of Recognized Period Costs	Total stock-based compensation expense included in the Consolidated Statements of Operations is as follows (in thousands): Year Ended 2017 2016 2015 Cost of revenue $ 1,739 $ 1,057 $ 871 Marketing 1,933 971 560 Product development 8,274 5,079 2,860 General and administrative 14,613 8,794 6,550 Total stock-based compensation expense $ 26,559 $ 15,901 $ 10,841

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	The following are the domestic and foreign components of the Company’s income (loss) before income taxes (in thousands): Year Ended 2017 2016 2015 Domestic $ (16,583 ) $ 25,910 $ 25,627 Foreign 48,848 (28,786 ) (53,621 ) Income (loss) before income taxes $ 32,265 $ (2,876 ) $ (27,994 )
Income Tax (Benefit) Provision	The income tax (benefit) provision is comprised of the following (in thousands): Year Ended 2017 2016 2015 Current: Federal $ (6,397 ) $ 22,084 $ 24,524 State 79 2,623 3,843 Foreign 476 580 579 Total current (5,842 ) 25,287 28,946 Deferred: Federal (34,948 ) 2,008 (2,863 ) State (8,778 ) (247 ) 108 Foreign 33 (23 ) (122 ) Total deferred (43,693 ) 1,738 (2,877 ) Total income tax (benefit) provision $ (49,535 ) $ 27,025 $ 26,069
Reconciliation of the Income Tax (Benefit) Provision	A reconciliation of the income tax (benefit) provision at the U.S. federal statutory income tax rate of 35% to the Company’s total income tax (benefit) provision is as follows (in thousands): Year Ended 2017 2016 2015 Income tax benefit at federal statutory rate $ 11,308 $ (1,007 ) $ (9,798 ) State and local taxes net of federal benefit (691 ) 1,545 2,575 Foreign income tax rate differential (11,878 ) 5,849 11,584 Stock-based compensation (12,584 ) 1,412 1,571 Net unrealized loss on warrant and other liabilities — — 1,097 Non-deductible items 168 267 1,314 Uncertain tax positions 789 4,033 5,523 Return to provision adjustment 167 (498 ) (25 ) Non-deductible acquisition costs — 199 10 Change in valuation allowance (4,673 ) 4,911 7,957 Research and development credit (1,098 ) (2,170 ) (7,684 ) Deferred charge on restructuring — 12,168 12,168 U.S. tax reform (31,063 ) — — Other 20 316 (223 ) Total income tax (benefit) provision $ (49,535 ) $ 27,025 $ 26,069
Significant Components of Deferred Tax Assets and Liabilities	Significant components of the Company’s deferred tax assets (liabilities) are as follows (in thousands): As of December 31, 2017 2016 Deferred tax assets: Net operating loss carryforwards $ 17,431 $ 13,084 Research and development credit carryforwards 3,597 898 Stock-based compensation expense 3,776 5,692 Accrued VAT liability 42 68 Alternative minimum tax credit 274 274 Allowance for doubtful accounts 384 611 Deferred rent 573 644 Accrued vacation 623 1,035 Unrealized loss on foreign currency 527 — Other, net 1,691 1,418 Total deferred tax assets 28,918 23,724 Less valuation allowance 11,021 13,839 Total net deferred tax asset 17,897 9,885 Deferred tax liabilities: Depreciation (6,850 ) (6,618 ) Global corporate restructuring liability (33,783 ) (64,460 ) Unrealized gain on foreign currency — (1,059 ) Other liabilities (891 ) (2,816 ) Total deferred tax liabilities (41,524 ) (74,953 ) Net deferred tax liabilities $ (23,627 ) $ (65,068 )
Summary of Valuation Allowance	The following table summarizes the valuation allowance activity for the periods indicated (in thousands): Year Ended 2017 2016 2015 Balance as of the beginning of period $ 13,839 $ 9,540 $ 1,892 Additions charged to expense — 4,886 7,983 Deletions credited to expense (4,691 ) — — Currency translation 1,873 (587 ) (335 ) Balance as of the end of period $ 11,021 $ 13,839 $ 9,540
Schedule of Unrecognized Tax Benefits Activity	The following table summarizes the unrecognized tax benefit activity for the periods indicated (in thousands): As of December 31, 2017 2016 2015 Balance as of the beginning of period $ 23,574 $ 22,229 $ 398 Additions based on tax positions related to the current year 732 1,071 21,797 Additions for tax positions of prior years 118 274 34 Reductions for tax provisions of prior years (7,411 ) — — Balance as of the end of period $ 17,013 $ 23,574 $ 22,229

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table presents the calculation of basic and diluted net income (loss) per share for periods presented (in thousands except share and per share amounts): Year Ended 2017 2016 2015 Numerator: Net income (loss) $ 81,800 $ (29,901 ) $ (54,063 ) Net income (loss) allocated to participating securities under the two-class method (80 ) — — Net income (loss) applicable to common stockholders—basic 81,720 (29,901 ) (54,063 ) Dilutive effect of net income allocated to participating securities under the two-class method 80 — — Change in fair value of liability classified restricted stock 771 — — Net income (loss) applicable to common stockholders—diluted $ 82,571 $ (29,901 ) $ (54,063 ) Denominator: Weighted average common shares outstanding—basic (1) 118,538,687 113,562,738 91,122,291 Common equivalent shares from options to purchase common stock and restricted stock units 2,498,448 — — Dilutive effect of assumed conversion of restricted stock units 1,177,799 — — Diluted effective of assumed conversion of restricted stock from acquisition 52,739 — — Weighted average common shares outstanding—diluted 122,267,673 113,562,738 91,122,291 Net income (loss) per share applicable to common stockholders—basic $ 0.69 $ (0.26 ) $ (0.59 ) Net income (loss) per share applicable to common stockholders—diluted $ 0.68 $ (0.26 ) $ (0.59 ) (1) 114,963 shares of unvested stock are considered participating securities and are excluded from basic shares outstanding for the year ended December 31, 2017 .
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following potential common shares were excluded from the calculation of diluted net income (loss) per share attributable to common stockholders because their effect would have been anti-dilutive for the periods presented: Year Ended 2017 2016 2015 Stock options 4,902,664 10,041,403 11,806,620 Restricted stock units 435,358 2,043,544 128,200 Warrants — 33,447 182,031 Convertible preferred stock — — 16,254,123 Total anti-dilutive securities 5,338,022 12,118,394 28,370,974

Segment and Geographic Inform35

Segment and Geographic Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Revenue from External Customers by Geographic Areas	The following table summarizes revenue, income (loss) before income taxes and net income (loss) by geographic area (in thousands): Year Ended 2017 2016 2015 United States $ 317,755 $ 276,537 $ 213,389 International 123,476 88,430 60,110 Revenue $ 441,231 $ 364,967 $ 273,499 United States $ (44,931 ) $ 7,926 $ 11,973 International 77,196 (10,802 ) (39,967 ) Income (loss) before income taxes $ 32,265 $ (2,876 ) $ (27,994 ) United States $ 5,113 $ (18,542 ) $ (13,639 ) International 76,687 (11,359 ) (40,424 ) Net income (loss) $ 81,800 $ (29,901 ) $ (54,063 )

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments Under Current Capital, Operating and Build-to-Suit Lease Agreements	The following table represents the Company’s commitments under its current capital, operating and build-to-suit lease agreements and purchase obligations as of December 31, 2017 (in thousands): Capital Lease Operating Build-to-Suit Purchase Obligations Periods ending 2018 $ 6,697 $ 3,907 $ 9,381 $ 14,320 2019 3,556 3,912 9,451 13,332 2020 918 3,566 9,522 16,677 2021 — 2,819 10,354 16,000 2022 — 2,608 10,520 17,000 Thereafter — 8,168 38,314 — Total minimum payments required $ 11,171 $ 24,980 $ 87,542 $ 77,329 Amounts representing interest 1,258 Present value of net minimum payments 9,913 Current maturities 5,798 Long-term payment obligations $ 4,115

Basis of Presentation and Sum37

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details)	Apr. 21, 2015USD ($)$ / sharesshares	Mar. 25, 2015	Dec. 31, 2017USD ($)reportable_segmentoperating_segment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from initial public offering			$ 0	$ 0	$ 199,467,000
Reverse stock split conversion ratio		0.5
Asset impairment charges			3,162,000	551,000	0
Amortization of deferred tax charge			(47,972,000)	2,194,000	(4,146,000)
Net cash provided by operating activities			67,420,000	49,994,000	33,155,000
Net cash provided by financing activities			$ 3,439,000	2,575,000	195,664,000
Fee for each completed transaction, percent			3.50%
Listing fee per item (usd per item)			$ 0.20
Period over which listing fee is recognized			4 months
Facility financing obligation			$ 60,049,000	57,360,000
Goodwill impairment			$ 0	0	0
Intangible asset, useful life			3 years
Advertising expense			$ 78,400,000	55,500,000	46,900,000
Number of operating segments | operating_segment			1
Number of reportable segments | reportable_segment			1
Excess tax benefit			$ 12,800,000
Cumulative effect on beginning retained earnings				(51,364,000)
IPO
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued (in shares) | shares	13,333,333
Share price (in dollars per share) | $ / shares	$ 16
Proceeds from initial public offering	$ 194,400,000
Underwriting discount	13,900,000
Other offering expense	$ 5,100,000
Sale of stock by stockholders (in shares) | shares	5,833,332
Conversion of preferred stock warrants into common stock warrants (in shares) | shares	203,030
Convertible preferred stock | IPO
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion of convertible preferred stock into common stock (in shares) | shares	53,448,243
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Direct checkout fees, percent			3.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Direct checkout fees, percent			4.00%
Software
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated useful lives			3 years
Software | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated useful lives			1 year
Software | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated useful lives			3 years
Accounting Standards Update 2016-09
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net cash provided by operating activities				3,200,000	3,900,000
Net cash provided by financing activities				$ (3,200)	$ (3,900)
Accounting Standards Update 2016-16
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative effect on beginning retained earnings			$ 51,400,000
Deferred tax assets			21,700,000
Adjustments for New Accounting Principle, Early Adoption | Accounting Standards Update 2016-16
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amortization of deferred charges related to deferred tax liability			$ 17,100,000

Basis of Presentation and Sum38

Basis of Presentation and Summary of Significant Accounting Policies - Summary of Revenue by Type of Service (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Product Information [Line Items]
Revenue	$ 441,231	$ 364,967	$ 273,499
Marketplace
Product Information [Line Items]
Revenue	179,492	158,204	132,648
Seller Services
Product Information [Line Items]
Revenue	258,453	200,857	136,608
Other
Product Information [Line Items]
Revenue	$ 3,286	$ 5,906	$ 4,243

Basis of Presentation and Sum39

Basis of Presentation and Summary of Significant Accounting Policies - Summary of Allowance Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance as of the beginning of period	$ 1,999	$ 2,071	$ 1,841
Bad debt expense	2,497	1,770	1,780
Write-offs, net of recoveries and other adjustments	(1,809)	(1,842)	(1,550)
Balance as of the end of period	$ 2,687	$ 1,999	$ 2,071

Business Combinations - Additio

Business Combinations - Additional Information (Details) - USD ($) $ in Thousands	Sep. 19, 2016	Feb. 28, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Intangible asset, useful life			3 years
Stock-based compensation expense—acquisitions			$ 3,904	$ 2,733	$ 1,860
Amortization expense of intangible assets			3,400	3,300	$ 2,200
Blackbird Technologies, Inc.
Business Acquisition [Line Items]
Common stock, value, outstanding	$ 32,500
Total purchase consideration	15,016
Cash paid	$ 8,050
Stock issued during period, issued for services (in shares)	184,230
Stock issued during period, value, issued for services	$ 2,500
Vesting period	3 years	3 years
Contingent consideration, liability	$ 8,800
Cash and equivalents acquired	$ 200
Finite-lived intangibles			8,500
Loss of acquirees since acquisition date			(9,200)	(2,400)
Stock-based compensation expense—acquisitions			5,800
Amortization expense of intangible assets			$ 3,000
Common Stock | Blackbird Technologies, Inc.
Business Acquisition [Line Items]
Number of shares issued for business acquisition (in shares)	513,304
Equity interest value assigned	$ 6,900
Developed Technology | Blackbird Technologies, Inc.
Business Acquisition [Line Items]
Finite-lived intangibles	$ 7,200
Intangible asset, useful life	3 years
Customer relationships | Blackbird Technologies, Inc.
Business Acquisition [Line Items]
Finite-lived intangibles	$ 1,250
Intangible asset, useful life	6 months
General and administrative | Blackbird Technologies, Inc.
Business Acquisition [Line Items]
Acquisition related costs				$ 600
Restricted stock units | Blackbird Technologies, Inc.
Business Acquisition [Line Items]
Number of shares issued for business acquisition (in shares)		460,575
Equity interest value assigned		$ 6,200

Business Combinations - Compone

Business Combinations - Components of the Purchase Price Allocation (Details) - USD ($) $ in Thousands	Sep. 19, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill		$ 38,541	$ 35,657	$ 27,752
Blackbird Technologies, Inc.
Business Acquisition [Line Items]
Cash paid	$ 8,050
Total purchase consideration	15,016
Working capital	81
Finite-lived intangibles		$ 8,500
Goodwill	8,660
Deferred tax liability	(2,175)
Net assets acquired	15,016
Blackbird Technologies, Inc. | Developed Technology
Business Acquisition [Line Items]
Finite-lived intangibles	7,200
Blackbird Technologies, Inc. | Customer relationships
Business Acquisition [Line Items]
Finite-lived intangibles	1,250
Blackbird Technologies, Inc. | Common Stock
Business Acquisition [Line Items]
Common shares	$ 6,966

Business Combinations - Summary

Business Combinations - Summary of Unaudited Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Business Combinations [Abstract]
Revenue	$ 365,786	$ 273,616
Net loss	$ (35,401)	$ (65,106)
Basic and diluted net (loss) income per share (in dollars per share)	$ (0.31)	$ (0.71)

Restructuring and Other Exit 43

Restructuring and Other Exit Costs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)position	Dec. 31, 2015USD ($)
Restructuring Cost and Reserve [Line Items]
Expected number of positions eliminated | position		245
Number of positions eliminated (as a percentage)		23.00%
Restructuring costs	$ 13,897	$ 0	$ 0
Expected cost remaining	800
Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring costs	10,200
Stock Modification
Restructuring Cost and Reserve [Line Items]
Restructuring costs	2,700
Other Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 1,000

Restructuring and Other Exit 44

Restructuring and Other Exit Costs - Schedule of Restructuring Reserve (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017
Restructuring Reserve [Roll Forward]
Restructuring reserve at period start	$ 3,440	$ 7,204	$ 0
Total restructuring and other exit costs	871	1,766	11,260
Costs charged against equity/assets	(354)	(965)	(1,668)
Cash payments	(2,615)	(4,565)	(2,388)
Restructuring reserve at period end	1,342	3,440	7,204
Employee Severance
Restructuring Reserve [Roll Forward]
Restructuring reserve at period start	3,348	6,862	0
Total restructuring and other exit costs	361	871	8,972
Costs charged against equity/assets	0	0	0
Cash payments	(2,401)	(4,385)	(2,110)
Restructuring reserve at period end	1,308	3,348	6,862
Stock Modification
Restructuring Reserve [Roll Forward]
Restructuring reserve at period start	0	0	0
Total restructuring and other exit costs	68	965	1,668
Costs charged against equity/assets	(68)	(965)	(1,668)
Cash payments	0	0	0
Restructuring reserve at period end	0	0	0
Other Restructuring
Restructuring Reserve [Roll Forward]
Restructuring reserve at period start	92	342	0
Total restructuring and other exit costs	442	(70)	620
Costs charged against equity/assets	(286)	0	0
Cash payments	(214)	(180)	(278)
Restructuring reserve at period end	$ 34	$ 92	$ 342

Restructuring and Other Exit 45

Restructuring and Other Exit Costs - Restructuring and Other Related Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 13,897	$ 0	$ 0
Cost of revenue
Restructuring Cost and Reserve [Line Items]
Restructuring costs	738	0	0
Marketing
Restructuring Cost and Reserve [Line Items]
Restructuring costs	2,950	0	0
Product development
Restructuring Cost and Reserve [Line Items]
Restructuring costs	3,232	0	0
General and administrative
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 6,977	$ 0	$ 0

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Major Categories of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 241,146	$ 103,108
Short-term investments	25,108	100,494
Receivables	14,144
Asset	280,398	203,602
Liability		2,067
Post-combination compensation classified as liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liability		2,067
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	11,290	2,997
Short-term investments	2,998	17,146
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	204,867	98,161
Receivables	14,144
U.S. Government bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	24,989	1,950
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	12,748	33,303
U.S. Government and agency bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	9,362	50,045
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	229,856	100,111
Short-term investments	9,362	50,045
Receivables	14,144
Asset	253,362	150,156
Liability		0
Level 1 | Post-combination compensation classified as liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liability		0
Level 1 | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term investments	0	0
Level 1 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	204,867	98,161
Receivables	14,144
Level 1 | U.S. Government bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	24,989	1,950
Level 1 | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Level 1 | U.S. Government and agency bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	9,362	50,045
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	11,290	2,997
Short-term investments	15,746	50,449
Receivables	0
Asset	27,036	53,446
Liability		0
Level 2 | Post-combination compensation classified as liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liability		0
Level 2 | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	11,290	2,997
Short-term investments	2,998	17,146
Level 2 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Receivables	0
Level 2 | U.S. Government bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 2 | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	12,748	33,303
Level 2 | U.S. Government and agency bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term investments	0	0
Receivables	0
Asset	0	0
Liability		2,067
Level 3 | Post-combination compensation classified as liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liability		2,067
Level 3 | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term investments	0	0
Level 3 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Receivables	0
Level 3 | U.S. Government bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 3 | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Level 3 | U.S. Government and agency bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 0	$ 0

Fair Value Measurements - Sch47

Fair Value Measurements - Schedule of Unobservable Inputs Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 2,067	$ 2,357
Changes to liability-classified stock awards	771	1,652
Conversion of liability-classified instruments to equity	(2,838)	(1,942)
Balance at end of period	$ 0	$ 2,067

Marketable Securities (Details)

Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 61,384	$ 103,520
Gross Unrealized Holding Loss	(8)	(31)
Gross Unrealized Holding Gain	11	2
Fair Value	61,387	103,491
Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Cost	36,280	2,997
Gross Unrealized Holding Loss	(1)	0
Gross Unrealized Holding Gain	0	0
Fair Value	36,279	2,997
Cash Equivalents | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Cost	11,290
Gross Unrealized Holding Loss	0
Gross Unrealized Holding Gain	0
Fair Value	11,290
Cash Equivalents | U.S. Government and agency bills
Schedule of Available-for-sale Securities [Line Items]
Cost	24,990	2,997
Gross Unrealized Holding Loss	(1)	0
Gross Unrealized Holding Gain	0	0
Fair Value	24,989	2,997
Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Cost	25,104	100,523
Gross Unrealized Holding Loss	(7)	(31)
Gross Unrealized Holding Gain	11	2
Fair Value	25,108	100,494
Short-term Investments | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Cost	2,998	17,146
Gross Unrealized Holding Loss	0	0
Gross Unrealized Holding Gain	0	0
Fair Value	2,998	17,146
Short-term Investments | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Cost	12,754	33,318
Gross Unrealized Holding Loss	(6)	(16)
Gross Unrealized Holding Gain	0	1
Fair Value	12,748	33,303
Short-term Investments | U.S. Government and agency bills
Schedule of Available-for-sale Securities [Line Items]
Cost	9,352	50,059
Gross Unrealized Holding Loss	(1)	(15)
Gross Unrealized Holding Gain	11	1
Fair Value	$ 9,362	$ 50,045

Property and Equipment - Summar

Property and Equipment - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 183,843	$ 172,560
Less: Accumulated depreciation and amortization	66,226	46,153
Property and equipment, net	$ 117,617	126,407
Computer equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Property and equipment, gross	$ 35,587	30,378
Furniture and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 6,194	5,920
Furniture and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	2 years
Furniture and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	4 years
Software
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Property and equipment, gross	$ 908	856
Software | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	1 year
Software | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 10,929	10,155
Building
Property, Plant and Equipment [Line Items]
Estimated useful lives	25 years
Property and equipment, gross	$ 81,892	81,957
Website development
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Property and equipment, gross	$ 48,333	$ 43,294

Property and Equipment - Summ50

Property and Equipment - Summary of Capitalized Website Development and Internal-Use Software Activities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Capitalized Computer Software, Net [Roll Forward]
Balance as of the beginning of the period	$ 43,294	$ 33,469
Additions to website development, excluding stock-based compensation	10,028	11,769
Additions to website development—stock-based compensation	807	792
Less: Retirements	625	2,736
Less: Impairments	5,171	0
Balance as of the end of the period	48,333	43,294	$ 33,469
Accumulated amortization balance as of the beginning of the period	24,155	19,676
Amortization Expense	8,209	6,333	7,300
Less: Retirements	364	1,854
Less: Impairments	2,009	0
Accumulated amortization balance as of the end of the period	29,991	24,155	$ 19,676
Capitalized Computer Software, Net	$ 18,342	$ 19,139

Property and Equipment - Additi

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation	$ 23,800	$ 19,200	$ 16,300
Amortization expense for equipment acquired under capital leases	7,700	6,300	3,800
Gross balance of leased equipment	27,700	22,300
Accumulated amortization of equipment under capital leases	18,600	10,900
Amortization Expense	8,209	6,333	7,300
Website development and internal-use software assets
Property, Plant and Equipment [Line Items]
Loss on write-off of retired website development and internal-use software	300	$ 900	$ 1,300
Impairment loss	$ 3,200

Goodwill and Intangible Asset52

Goodwill and Intangible Assets - Summary of Changes in the Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Balance as of the beginning of the period	$ 35,657	$ 27,752
Acquisitions	0	8,660
Other adjustments	2,884	(755)
Balance as of the end of the period	$ 38,541	$ 35,657

Goodwill and Intangible Asset53

Goodwill and Intangible Assets - Summary of Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 19, 2016	Jun. 30, 2014	Apr. 30, 2014
Finite-Lived Intangible Assets [Line Items]
Gross book value	$ 7,200	$ 11,716
Accumulated amortization	(3,100)	(4,209)
Total amortization expense	4,100	7,507
Amortization expense of intangible assets	3,400	3,300	$ 2,200
Technology
Finite-Lived Intangible Assets [Line Items]
Gross book value	7,200	10,466
Accumulated amortization	(3,100)	(3,536)
Total amortization expense	4,100	6,930
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross book value	0	1,250
Accumulated amortization	0	(673)
Total amortization expense	0	$ 577
Blackbird Technologies, Inc.
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangibles	8,500
Amortization expense of intangible assets	$ 3,000
Blackbird Technologies, Inc. | Technology
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangibles				$ 7,200
Blackbird Technologies, Inc. | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangibles				$ 1,250
ALM [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangibles					$ 4,100
Jarvis Labs, Inc [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangibles						$ 2,800

Goodwill and Intangible Asset54

Goodwill and Intangible Assets - Summary of Future Amortization Expense for Intangible Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill impairment	$ 0	$ 0	$ 0
Impairment of intangible assets	0
Asset impairment charges	3,162,000	551,000	$ 0
2,017	2,400,000
2,018	1,700,000
Thereafter	0
Total amortization expense	$ 4,100,000	$ 7,507,000

Debt (Details)

Debt (Details) - Revolving Credit Facility - USD ($)	Nov. 21, 2017	Mar. 31, 2015	May 31, 2014
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity		$ 50,000,000	$ 35,000,000
Outstanding borrowings	$ 0
Letter of Credit
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity			10,000,000
Bridge Loan
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity			$ 15,000,000

Warrants - Additional Informati

Warrants - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	May 31, 2016	Oct. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Apr. 21, 2015
Class of Stock [Line Items]
Net unrealized loss on warrant and other liabilities			$ 0	$ 0	$ 3,133
Warrants
Class of Stock [Line Items]
Net unrealized loss on warrant and other liabilities					$ 3,100
Common Stock
Class of Stock [Line Items]
Warrants exercised in period net of forfeitures (in shares)	80,011	96,869
Exercise of warrants (in shares)	97,931	105,099
Exercise price of warrant (in dollars per share)	$ 1.62	$ 1.03
Share price (in dollars per share)	$ 8.88	$ 12.90
Warrants forfeited (in shares)	17,920	8,230
IPO
Class of Stock [Line Items]
Exercise price of warrant (in dollars per share)						$ 24.97
Conversion of preferred stock warrants into common stock warrants (in shares)						203,030
Fair value adjustment of warrants						$ 5,100

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock (Details)	12 Months Ended
	Dec. 31, 2017USD ($)vote$ / sharesshares	Dec. 31, 2016$ / sharesshares	Dec. 31, 2015shares	Dec. 31, 2014shares
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	1,400,000,000	1,400,000,000
Preferred stock, shares authorized (in shares)	25,000,000	25,000,000
Common stock, shares outstanding (in shares)	121,769,238	115,973,039
Common stock, votes per share of stock held | vote	1
Dividends declared for common stock | $	$ 0
Common stock, par value (in dollars per share) | $ / shares	$ 0.001	$ 0.001
Common Stock
Class of Stock [Line Items]
Shares issued (in shares)	121,769,238	115,973,039	112,563,354	44,180,939

Stockholders' Equity - Converti

Stockholders' Equity - Convertible Preferred Stock (Details) - shares	Apr. 21, 2015	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Convertible preferred stock
Class of Stock [Line Items]
Shares Outstanding (in shares)		0	0	0
Common Stock
Class of Stock [Line Items]
Conversion of preferred stock upon public offering (in shares)	53,448,243	53,448,243

Stockholders' Equity - Common59

Stockholders' Equity - Common Stock Issuances (Details) - Jarvis Labs, Inc. and Incubart SAS $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)shares
Class of Stock [Line Items]
Shares issued in connection with acquisitions (in shares)	685,749
Shares issued (in shares)	172,445
Fair value of shares issued | $	$ 2.3
Common Stock
Class of Stock [Line Items]
Number of shares issued for business acquisition (in shares)	513,304
Equity interest value assigned | $	$ 6.9

Stockholders' Equity - Share Re

Stockholders' Equity - Share Repurchase Program (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2017	Nov. 17, 2017	Dec. 31, 2017	Dec. 31, 2017
Equity [Abstract]
Stock repurchase (in shares)	586,231	0	586,231
Average cost per share (in dollars per share)	$ 17.57	$ 0	$ 17.57
Stock repurchase	$ (10,301)	$ 0	$ (10,301)	$ (10,301)
Remaining authorized repurchase amount	$ 89,699		$ 89,699	$ 89,699
Authorized repurchase amount		$ 100,000

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Details) - USD ($) $ in Thousands	Jan. 02, 2018	Jan. 03, 2017	Jan. 04, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense—acquisitions				$ 3,904	$ 2,733	$ 1,860
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation for stock options				$ 23,700
Weighted-average period for unrecognized compensation				3 years 2 months 16 days
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average period for unrecognized compensation				2 years 8 months 16 days
Unrecognized compensation for restricted stock units				$ 30,100
2006 Stock Plan | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term for options				10 years
2015 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of additional shares issued annually		5,798,651	2,814,083	7,050,000
Percentage of outstanding stock				5.00%
Shares reserved for future issuance				14,100,000
Number of shares authorized				23,347,913
Number of shares available for grant				14,355,379
2015 Equity Incentive Plan | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term for options				10 years
Stock option vesting period				4 years
Stock option requisite service period				4 years
2015 Equity Incentive Plan | Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period				4 years
2006 Plan Eligible for 2015 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance				12,653,075
25% Vest After First Year of Service | 2006 Stock Plan | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting rights, percentage				25.00%
25% Vest After First Year of Service | 2015 Equity Incentive Plan | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting rights, percentage				25.00%
25% Vest After First Year of Service | 2015 Equity Incentive Plan | Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting rights, percentage				25.00%
Vest Ratably Each Month Over a 36-Month Period | 2006 Stock Plan | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period				36 months
Vest Ratably Each Month Over a 36-Month Period | 2015 Equity Incentive Plan | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period				36 months
Newly-Hired Employee | Vest Ratably Each Month Over a 36-Month Period | 2015 Equity Incentive Plan | Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period				3 years
Current Employee | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period				48 months
Current Employee | 2015 Equity Incentive Plan | Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period				4 years
Subsequent Event | 2015 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of additional shares issued annually	6,088,461

Stock-based Compensation - Fair

Stock-based Compensation - Fair Value of Options Granted Using the Black-Scholes Pricing Model (Details) - Stock options	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility, minimum	41.70%	38.60%	40.40%
Volatility, maximum	44.20%	44.60%	45.00%
Risk-free interest rate, minimum	1.90%	1.10%	1.30%
Risk-free interest rate, maximum	2.20%	2.10%	1.90%
Dividend rate	0.00%	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years 6 months	5 years 6 months
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 3 months 18 days	6 years 3 months 18 days	6 years 1 month 6 days

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shares
Outstanding, beginning balance (in shares)	9,339,567	11,068,859	11,525,279
Granted (in shares)	5,887,183	1,700,234	1,660,170
Exercised (in shares)	(5,760,263)	(2,535,620)	(1,315,735)
Forfeited/Cancelled (in shares)	(1,518,548)	(893,906)	(800,855)
Outstanding, ending balance (in shares)	7,947,939	9,339,567	11,068,859	11,525,279
Total exercisable at December 31, 2017 (in shares)	2,294,818
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per share)	$ 7.89	$ 6.94	$ 5.34
Granted (in dollars per share)	11.04	9.35	16.19
Exercised (in dollars per share)	5.87	4.17	2.76
Forfeited/Cancelled (in dollars per share)	11.36	9.51	9.94
Outstanding, ending balance (in dollars per share)	11.02	$ 7.89	$ 6.94	$ 5.34
Total exercisable at December 31, 2017 (in dollars per share)	$ 10.48
Weighted-Average Remaining Contract Term (in years)
Outstanding, Weighted-Average Remaining Contract Term	7 years 11 months 5 days	6 years 7 months 21 days	7 years 4 days	7 years 6 months 25 days
Total exercisable at December 31, 2017, Weighted-Average Remaining Contract Term	4 years 9 months 23 days
Aggregate Intrinsic Value
Outstanding, Aggregate Intrinsic Value	$ 74,996	$ 43,613	$ 31,932	$ 134,386
Total exercisable at December 31, 2017, Aggregate Intrinsic Value	$ 22,912

Stock-based Compensation - Weig

Stock-based Compensation - Weighted Average Grant Date Fair Value Options Granted and Awards Vested and Intrinsic Value of Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Weighted average grant date fair value of options granted (in shares)	$ 4.85	$ 4.03	$ 6.89
Intrinsic value of options exercised	$ 52,693	$ 19,130	$ 15,148
Fair value of awards vested	$ 19,826	$ 9,533	$ 8,337

Stock-based Compensation - Su65

Stock-based Compensation - Summary of the Unvested RSUs (Details) - RSUs - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Unvested at beginning of period (in shares)	3,135,181	395,846	0
Granted (in shares)	2,360,315	3,200,297	407,368
Vested (in shares)	(1,072,321)	(255,868)	0
Forfeited/Canceled (in shares)	(1,348,928)	(205,094)	(11,522)
Unvested at period end (in shares)	3,074,247	3,135,181	395,846
Weighted-Average Fair Value
Unvested at beginning of period (in dollars per share)	$ 10.70	$ 13.70	$ 0
Granted (in dollars per share)	12.17	10.29	13.78
Vested (in dollars per share)	10.44	10.64	0
Forfeited/Canceled (in dollars per share)	10.56	10.15	16.76
Unvested at period end (in dollars per share)	$ 11.98	$ 10.70	$ 13.70

Stock-based Compensation - Allo

Stock-based Compensation - Allocated Share-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 26,559	$ 15,901	$ 10,841
Cost of revenue
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	1,739	1,057	871
Marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	1,933	971	560
Product development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	8,274	5,079	2,860
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 14,613	$ 8,794	$ 6,550

Income Taxes - Domestic and For

Income Taxes - Domestic and Foreign Components of (Loss) Income Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Domestic	$ (16,583)	$ 25,910	$ 25,627
Foreign	48,848	(28,786)	(53,621)
Income (loss) before income taxes	$ 32,265	$ (2,876)	$ (27,994)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
U.S. federal statutory income tax rate	35.00%
Alternative minimum tax credit	$ 274	$ 274
Research and development credit carryforwards	3,597	898
Valuation allowance	11,021	13,839
Deferred tax assets considered realizable	17,897	9,885
Unrecognized tax benefits	17,013	23,574	$ 22,229		$ 398
Unrecognized tax benefits that would impact effective tax rate favorably	17,000
Deferred tax liability for gain in revised corporate structure transaction	41,524	74,953
Deferred tax assets	28,918	23,724
U.S. tax reform	(31,063)	0	0
Excess tax benefit	12,800
Global Corporate Structure
Income Tax Contingency [Line Items]
Deferred tax liability for gain in revised corporate structure transaction				$ 66,000
Deferred tax assets				$ 66,000
Additional Paid-in Capital
Income Tax Contingency [Line Items]
Excess tax deductions on share-based compensation		3,200	$ 3,900
Internal Revenue Service (IRS)
Income Tax Contingency [Line Items]
Alternative minimum tax credit	300	300
Research and development credit carryforwards	$ 3,600	$ 900
Foreign Tax Authority
Income Tax Contingency [Line Items]
Term of cumulative foreign loss	3 years

Income Taxes - Income Tax (Bene

Income Taxes - Income Tax (Benefit) Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ (6,397)	$ 22,084	$ 24,524
State	79	2,623	3,843
Foreign	476	580	579
Total current	(5,842)	25,287	28,946
Deferred:
Federal	(34,948)	2,008	(2,863)
State	(8,778)	(247)	108
Foreign	33	(23)	(122)
Total deferred	(43,693)	1,738	(2,877)
Total income tax (benefit) provision	$ (49,535)	$ 27,025	$ 26,069

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of the Income Tax (Benefit) Provision at the U.S. Federal Statutory Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income tax benefit at federal statutory rate	$ 11,308	$ (1,007)	$ (9,798)
State and local taxes net of federal benefit	(691)	1,545	2,575
Foreign income tax rate differential	(11,878)	5,849	11,584
Stock-based compensation	(12,584)	1,412	1,571
Net unrealized loss on warrant and other liabilities	0	0	1,097
Non-deductible items	168	267	1,314
Uncertain tax positions	789	4,033	5,523
Return to provision adjustment	167	(498)	(25)
Non-deductible acquisition costs	0	199	10
Change in valuation allowance	(4,673)	4,911	7,957
Research and development credit	(1,098)	(2,170)	(7,684)
Deferred charge on restructuring	0	12,168	12,168
U.S. tax reform	(31,063)	0	0
Other	20	316	(223)
Total income tax (benefit) provision	$ (49,535)	$ 27,025	$ 26,069

Income Taxes - Significant Comp

Income Taxes - Significant Component of Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 17,431	$ 13,084
Research and development credit carryforwards	3,597	898
Stock-based compensation expense	3,776	5,692
Accrued VAT liability	42	68
Alternative minimum tax credit	274	274
Allowance for doubtful accounts	384	611
Deferred rent	573	644
Accrued vacation	623	1,035
Unrealized loss on foreign currency	527	0
Other, net	1,691	1,418
Total deferred tax assets	28,918	23,724
Less valuation allowance	11,021	13,839
Total net deferred tax asset	17,897	9,885
Deferred tax liabilities:
Depreciation	(6,850)	(6,618)
Global corporate restructuring liability	(33,783)	(64,460)
Unrealized gain on foreign currency	0	(1,059)
Other liabilities	(891)	(2,816)
Total deferred tax liabilities	(41,524)	(74,953)
Net deferred tax liabilities	$ (23,627)	$ (65,068)

Income Taxes - Summary of Valua

Income Taxes - Summary of Valuation Allowance Activity (Details) - Valuation Allowance of Deferred Tax Assets - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance as of the beginning of period	$ 13,839	$ 9,540	$ 1,892
Additions charged to expense	0	4,886	7,983
Deletions credited to expense	(4,691)	0	0
Currency translation	1,873	(587)	(335)
Balance as of the end of period	$ 11,021	$ 13,839	$ 9,540

Income Taxes - Summary of Unrec

Income Taxes - Summary of Unrecognized Tax Benefits Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of the beginning of period	$ 23,574	$ 22,229	$ 398
Additions based on tax positions related to the current year	732	1,071	21,797
Additions for tax positions of prior years	118	274	34
Reductions for tax provisions of prior years	(7,411)	0	0
Balance as of the end of period	$ 17,013	$ 23,574	$ 22,229

Net Income (Loss) Per Share - C

Net Income (Loss) Per Share - Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income (loss)	$ 81,800	$ (29,901)	$ (54,063)
Net income (loss) allocated to participating securities under the two-class method	(80)	0	0
Net income (loss) applicable to common stockholders—basic	81,720	(29,901)	(54,063)
Dilutive effect of net income allocated to participating securities under the two-class method	80	0	0
Change in fair value of liability classified restricted stock	771	0	0
Net income (loss) applicable to common stockholders—diluted	$ 82,571	$ (29,901)	$ (54,063)
Denominator:
Weighted average common shares outstanding—basic (in shares)	118,538,687	113,562,738	91,122,291
Weighted average common shares outstanding—diluted (in shares)	122,267,673	113,562,738	91,122,291
Net income (loss) per share applicable to common stockholders—basic (in shares)	$ 0.69	$ (0.26)	$ (0.59)
Net income (loss) per share applicable to common stockholders—diluted (in shares)	$ 0.68	$ (0.26)	$ (0.59)
Anti-dilutive securities excluded from computation of earnings per share (in shares)	5,338,022	12,118,394	28,370,974
Equity Option [Member]
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	2,498,448	0	0
Restricted stock units
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	1,177,799	0	0
Restricted Stock [Member]
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	52,739	0	0
Participating Securities [Member]
Denominator:
Anti-dilutive securities excluded from computation of earnings per share (in shares)	114,963

Net Income (Loss) Per Share - S

Net Income (Loss) Per Share - Summary of Shares Excluded from the Calculation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share (in shares)	5,338,022	12,118,394	28,370,974
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share (in shares)	4,902,664	10,041,403	11,806,620
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share (in shares)	435,358	2,043,544	128,200
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share (in shares)	0	33,447	182,031
Convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share (in shares)	0	0	16,254,123

Segment and Geographic Inform76

Segment and Geographic Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)reportable_segmentoperating_segment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Segment Reporting [Abstract]
Number of reportable segments | reportable_segment	1
Number of operating segments | operating_segment	1
Revenue, Major Customer [Line Items]
Revenue	$ 441,231	$ 364,967	$ 273,499
Income (loss) before income taxes	32,265	(2,876)	(27,994)
Net income (loss)	81,800	(29,901)	(54,063)
United States
Revenue, Major Customer [Line Items]
Revenue	317,755	276,537	213,389
Income (loss) before income taxes	(44,931)	7,926	11,973
Net income (loss)	5,113	(18,542)	(13,639)
International
Revenue, Major Customer [Line Items]
Revenue	123,476	88,430	60,110
Income (loss) before income taxes	77,196	(10,802)	(39,967)
Net income (loss)	$ 76,687	$ (11,359)	$ (40,424)

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) ft² in Thousands	1 Months Ended	12 Months Ended
	May 31, 2014ft²	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Feb. 17, 2017USD ($)	Jan. 03, 2014USD ($)
Loss Contingencies [Line Items]
Gross balance of leased equipment		$ 27,700,000	$ 22,300,000
Capital leases, interest expense		1,600,000	1,600,000	$ 1,200,000
Operating leases, rent expense		4,100,000	6,000,000	5,100,000
Collateral account		5,341,000	5,341,000
Purchase obligation		77,329,000
Non-income Tax Obligations
Loss Contingencies [Line Items]
Non-income tax obligation reserve		400,000	$ 300,000
Capital Lease Obligations | Dell Financial Services, LLC
Loss Contingencies [Line Items]
Line of credit, maximum borrowing capacity		$ 9,000,000			$ 6,000,000
Term of lease		36 months
Buyout option		$ 1
Capital Lease Obligations | ePlus Group, Inc
Loss Contingencies [Line Items]
Line of credit, maximum borrowing capacity				$ 18,000,000		$ 8,000,000
Term of lease		36 months
Buyout option		$ 1
Capital Lease Obligations | TriplePoint Capital, LLC
Loss Contingencies [Line Items]
Line of credit, maximum borrowing capacity						$ 20,000,000
Term of lease		36 months
Interest rate percentage		8.25%
Office Building
Loss Contingencies [Line Items]
Build-to-suit leases, term of contract	10 years
Area of real estate property | ft²	199
Office Building | Build-to-Suit Lease
Loss Contingencies [Line Items]
Area of real estate property | ft²	172
Collateral account		$ 5,300,000
Office Building | Operating Lease
Loss Contingencies [Line Items]
Area of real estate property | ft²	27
Computer Equipment | Dell Financial Services, LLC
Loss Contingencies [Line Items]
Gross balance of leased equipment		4,800,000
Computer Equipment | ePlus Group, Inc
Loss Contingencies [Line Items]
Gross balance of leased equipment		$ 5,100,000
Minimum | Capital Lease Obligations | ePlus Group, Inc
Loss Contingencies [Line Items]
Interest rate percentage		3.50%
Maximum | Capital Lease Obligations | ePlus Group, Inc
Loss Contingencies [Line Items]
Interest rate percentage		6.93%

Commitments and Contingencies78

Commitments and Contingencies - Summary of Lease Commitments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Capital Lease Obligations
2,018	$ 6,697
2,019	3,556
2,020	918
2,021	0
2,022	0
Thereafter	0
Capital Leases, Future Minimum Payments Due	11,171
Amounts representing interest	1,258
Present value of net minimum payments	9,913
Current maturities	5,798	$ 6,829
Long-term payment obligations	4,115	$ 5,296
Operating Leases
2,018	3,907
2,019	3,912
2,020	3,566
2,021	2,819
2,022	2,608
Thereafter	8,168
Operating Leases, Future Minimum Payments Due	24,980
Build-to-Suit Lease
2,018	9,381
2,019	9,451
2,020	9,522
2,021	10,354
2,022	10,520
Thereafter	38,314
Build-to-Suit Leases, Future Minimum Payments Due	87,542
Purchase Obligations
2,018	14,320
2,019	13,332
2,020	16,677
2,021	16,000
2,022	17,000
Thereafter	0
Purchase Obligations, Future Minimum Payments Due	$ 77,329