Wayfair (W) 10-Q 2 Nov 17 2017 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Oct. 26, 2017
Document and Entity Information
Entity Registrant Name	Wayfair Inc.
Entity Central Index Key	1,616,707
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding Class A
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		56,541,838
Entity Common Stock, Shares Outstanding Class B
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		31,289,628

CONSOLIDATED AND CONDENSED BALA

CONSOLIDATED AND CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 553,721	$ 279,840
Short-term investments	56,699	68,743
Accounts receivable, net of allowance of $4,507 and $3,115 at September 30, 2017 and December 31, 2016, respectively	27,521	19,113
Inventories	18,613	18,550
Prepaid expenses and other current assets	120,041	90,845
Total current assets	776,595	477,091
Property and equipment, net	318,873	239,354
Goodwill and intangible assets, net	3,386	4,230
Long-term investments	29,809	30,967
Other noncurrent assets	9,477	10,041
Total assets	1,138,140	761,683
Current liabilities
Accounts payable	381,661	379,493
Accrued expenses	121,218	67,807
Deferred revenue	86,219	65,892
Other current liabilities	61,151	44,028
Total current liabilities	650,249	557,220
Lease financing obligation	82,725	28,900
Long-term debt	327,950	0
Other liabilities	74,187	96,179
Total liabilities	1,135,111	682,299
Commitments and contingencies (Note 6)
Convertible preferred stock, $0.001 par value per share: 10,000,000 shares authorized and none issued at September 30, 2017 and December 31, 2016	0	0
Additional paid-in capital	515,380	409,225
Accumulated deficit	(510,495)	(329,940)
Accumulated other comprehensive (loss) gain	(1,943)	13
Total stockholders’ equity	3,029	79,384
Total liabilities and stockholders’ equity	1,138,140	761,683
Class A common stock
Common stock	56	50
Class B common stock
Common stock	$ 31	$ 36

CONSOLIDATED AND CONDENSED BAL3

CONSOLIDATED AND CONDENSED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Accounts receivable allowance	$ 4,507	$ 3,115
Convertible redeemable preferred units, par value (in dollars per share)	$ 0.001	$ 0.001
Convertible redeemable preferred units, shares authorized (in shares)	10,000,000	10,000,000
Convertible redeemable preferred units, shares issued (in shares)	0	0
Class A common stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Common stock, shares outstanding (in shares)	56,355,606	49,945,202
Common stock, shares issued (in shares)	56,355,606	49,945,202
Class B common stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	164,000,000	164,000,000
Common stock, shares outstanding (in shares)	31,290,483	35,885,692
Common stock, shares issued (in shares)	31,290,483	35,885,692

CONSOLIDATED AND CONDENSED STAT

CONSOLIDATED AND CONDENSED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Net revenue	$ 1,198,198	$ 861,525	$ 3,281,879	$ 2,395,801
Cost of goods sold	917,889	659,864	2,495,221	1,826,570
Gross profit	280,309	201,661	786,658	569,231
Operating expenses:
Customer service and merchant fees	42,949	33,872	117,132	91,286
Advertising	141,714	101,333	384,220	293,436
Merchandising, marketing and sales	56,934	48,550	160,033	129,679
Operations, technology, general and administrative	112,669	79,526	292,988	207,289
Total operating expenses	354,266	263,281	954,373	721,690
Loss from operations	(73,957)	(61,620)	(167,715)	(152,459)
Interest (expense) income, net	(2,008)	(292)	(3,857)	791
Other (expense) income, net	(227)	889	400	1,804
Loss before income taxes	(76,192)	(61,023)	(171,172)	(149,864)
Provision for (benefit from) income taxes	237	(83)	671	555
Net loss	$ (76,429)	$ (60,940)	$ (171,843)	$ (150,419)
Net loss per share, basic and diluted (in dollars per share)	$ (0.88)	$ (0.72)	$ (1.98)	$ (1.77)
Weighted average number of common stock outstanding used in computing per share amounts, basic and diluted (in shares)	87,283	85,105	86,679	84,779

CONSOLIDATED AND CONDENSED STA5

CONSOLIDATED AND CONDENSED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net loss	$ (76,429)	$ (60,940)	$ (171,843)	$ (150,419)
Other comprehensive loss:
Foreign currency translation adjustments	(856)	(240)	(1,959)	(875)
Net unrealized (loss) gain on available-for-sale investments	(40)	(163)	3	465
Comprehensive loss	$ (77,325)	$ (61,343)	$ (173,799)	$ (150,829)

CONSOLIDATED AND CONDENSED STA6

CONSOLIDATED AND CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities
Net loss	$ (171,843)	$ (150,419)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	62,588	38,528
Equity based compensation	46,740	35,188
Amortization of discount and issuance costs on convertible notes	874	0
Other non-cash adjustments	913	(134)
Changes in operating assets and liabilities:
Accounts receivable	(8,697)	(6,773)
Inventories	(38)	716
Prepaid expenses and other current assets	(27,776)	(12,493)
Accounts payable and accrued expenses	44,692	53,443
Deferred revenue and other liabilities	50,450	33,556
Other assets	(1,148)	(2,292)
Net cash used in operating activities	(3,245)	(10,680)
Cash flows from investing activities
Purchase of short-term and long-term investments	(47,639)	(76,458)
Sale and maturities of short-term investments	60,540	82,060
Purchase of property and equipment	(76,528)	(81,844)
Site and software development costs	(34,885)	(21,444)
Cash received from the sale of a business, net of cash sold	0	1,508
Other investing activities, net	0	(1,000)
Net cash used in investing activities	(98,512)	(97,178)
Cash flows from financing activities
Proceeds from issuance of convertible notes, net of issuance costs	420,449	0
Premiums paid for capped call confirmations	(44,160)	0
Taxes paid related to net share settlement of equity awards	(1,277)	(18,426)
Net proceeds from exercise of stock options	213	166
Net cash provided by (used in) financing activities	375,225	(18,260)
Effect of exchange rate changes on cash and cash equivalents	413	286
Net increase (decrease) in cash and cash equivalents	273,881	(125,832)
Cash and cash equivalents
Beginning of period	279,840	334,176
End of period	553,721	208,344
Supplemental disclosure of non-cash investing activities
Purchase of property and equipment included in accounts payable and accrued expenses and in other liabilities	9,255	5,744
Construction costs capitalized under finance lease obligation and other leases	$ 16,153	$ 29,726

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation Wayfair Inc. (the “Company”) is one of the world's largest online destinations for the home. Through its e-commerce business model, the Company offers visually inspired browsing, compelling merchandising, easy product discovery and attractive prices for over eight million products from approximately 10,000 suppliers. The consolidated and condensed financial statements and other disclosures contained in this Quarterly Report on Form 10-Q are those of the Company. The consolidated and condensed balance sheet data as of December 31, 2016 was derived from audited financial statements. The accompanying consolidated and condensed balance sheet as of September 30, 2017 , the consolidated and condensed statements of operations, consolidated and condensed statements of comprehensive loss, and consolidated and condensed statements of cash flows for the periods ended September 30, 2017 and 2016 are unaudited. The unaudited interim financial statements have been prepared on the same basis as the audited consolidated financial statements and in the opinion of management, reflect all adjustments, consisting of only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of September 30, 2017 and statements of operations, comprehensive loss, and cash flows for the periods ended September 30, 2017 and 2016 . The financial data and the other information disclosed in these notes to the consolidated and condensed financial statements related to these periods are unaudited. The consolidated and condensed statements of operations, comprehensive loss, and cash flows for the period ended September 30, 2017 are not necessarily indicative of the results of operations and cash flows that may be expected for the year ending December 31, 2017 , or for any other period.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies The Company has identified the significant accounting policies that are critical to understanding its business and results of operations. The Company believes that there have been no significant changes during the nine months ended September 30, 2017 to the items disclosed in Note 2, Summary of Significant Accounting Policies , included in Part II, Item 8, Financial Statements and Supplementary Data , of the Company’s Annual Report on Form 10-K for the year ended December 31, 2016 .

Marketable Securities and Fair

Marketable Securities and Fair Value Measurements	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Marketable Securities and Fair Value Measurements	Marketable Securities and Fair Value Measurements Marketable Securities As of September 30, 2017 and December 31, 2016 , all of the Company’s marketable securities were classified as available-for-sale and their estimated fair values were $86.5 million and $99.7 million , respectively. The Company periodically reviews its available-for-sale securities for other-than-temporary impairment. The Company considers factors such as the duration, severity and the reason for the decline in value, the potential recovery period, and its intent to sell. As of September 30, 2017 , the Company’s available-for-sale securities primarily consisted of corporate bonds and other government obligations that are priced at fair value. During the three and nine months ended September 30, 2017 and 2016 , the Company did not recognize any other-than-temporary impairment losses. The maturities of the Company’s long-term marketable securities generally range from one to three years. The cost basis of a marketable security sold is determined by the Company using the specific identification method. During the three and nine months ended September 30, 2017 and 2016 , we did not have any realized gains or losses. The following tables present details of the Company’s marketable securities as of September 30, 2017 and December 31, 2016 (in thousands): September 30, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Short-term: Investment securities $ 56,719 $ 12 $ (32 ) $ 56,699 Long-term: Investment securities 29,837 22 (50 ) 29,809 Total $ 86,556 $ 34 $ (82 ) $ 86,508 December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Short-term: Investment securities $ 63,135 $ 7 $ (39 ) $ 63,103 Commercial paper 5,641 1 (2 ) 5,640 Long-term: Investment securities 30,985 16 (34 ) 30,967 Total $ 99,761 $ 24 $ (75 ) $ 99,710 Fair Value Measurements The Company's financial assets and liabilities are measured at fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). The three levels of inputs used to measure fair value are as follows: ▪ Level 1—Unadjusted quoted prices in active markets for identical assets or liabilities ▪ Level 2—Unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or inputs other than quoted prices that are observable or can be corroborated by observable market data for substantially the full-term of the asset or liability ▪ Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the asset or liability This hierarchy requires the Company to use observable market data, when available, and to minimize the use of unobservable inputs when determining fair value. The Company measures its cash equivalents and short-term and long-term investments at fair value. The Company classifies its cash equivalents and restricted cash within Level 1 because the Company values these investments using quoted market prices. The fair value of the Company's Level 1 financial assets is based on quoted market prices of the identical underlying security. The Company classifies short-term and long-term investments within Level 2 because unadjusted quoted prices for identical or similar assets in markets are not active. The Company does not have any assets or liabilities classified as Level 3 financial assets. The following tables set forth the fair value of the Company’s financial assets measured at fair value on a recurring basis as of September 30, 2017 and December 31, 2016 based on the three-tier value hierarchy (in thousands): September 30, 2017 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds and other funds $ 512,929 $ — $ — $ 512,929 Short-term investments: Investment securities — 56,699 — 56,699 Restricted cash: Certificate of deposit 5,000 — — 5,000 Long-term: Investment securities — 29,809 — 29,809 Total $ 517,929 $ 86,508 $ — $ 604,437 December 31, 2016 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 200,867 $ — $ — $ 200,867 Short-term investments: Investment securities — 63,103 — 63,103 Commercial paper — 5,640 — 5,640 Restricted cash: Certificate of deposit 5,000 — — 5,000 Long-term: Investment securities — 30,967 — 30,967 Total $ 205,867 $ 99,710 $ — $ 305,577

Intangible Assets and Goodwill

Intangible Assets and Goodwill	9 Months Ended
	Sep. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets and Goodwill	Intangible Assets and Goodwill The following table summarizes intangible assets as of September 30, 2017 and December 31, 2016 (in thousands): Weighted - Average Amortization Period (Years) September 30, 2017 Gross Carrying Amount Accumulated Amortization Net Book Value Trademarks 5 $ 1,900 $ (1,583 ) $ 317 Technology 3 1,453 (525 ) 928 Customer relationships 5 1,300 (1,083 ) 217 Total $ 4,653 $ (3,191 ) $ 1,462 Weighted - Average Amortization Period (Years) December 31, 2016 Gross Carrying Amount Accumulated Amortization Net Book Value Trademarks 5 $ 1,900 $ (1,298 ) $ 602 Technology 3 1,453 (161 ) 1,292 Customer relationship 5 1,300 (888 ) 412 Total $ 4,653 $ (2,347 ) $ 2,306 Amortization expense related to intangible assets was $0.3 million and $ 0.2 million for the three months ended September 30, 2017 and 2016 , respectively, and $0.8 million and $0.6 million for the nine months ended September 30, 2017 and 2016 , respectively. Goodwill as of September 30, 2017 was $1.9 million , unchanged from December 31, 2016 .

Property and Equipment, net

Property and Equipment, net	9 Months Ended
	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Property and Equipment, net	Property and Equipment, net The following table summarizes property and equipment, net as of September 30, 2017 and December 31, 2016 (in thousands): September 30, December 31, Furniture and computer equipment $ 198,903 $ 133,297 Site and software development costs 108,456 77,429 Leasehold improvements 80,512 62,090 Construction in progress 10,416 47,013 Buildings (leased - Note 6) 83,681 29,856 481,968 349,685 Less accumulated depreciation and amortization (163,095 ) (110,331 ) Property and equipment, net $ 318,873 $ 239,354 Property and equipment depreciation and amortization expense was $ 22.6 million and $15.2 million for the three months ended September 30, 2017 and 2016 , respectively, and $61.7 million and $37.9 million for the nine months ended September 30, 2017 and 2016 , respectively.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Leases The Company leases office and warehouse spaces under non-cancelable leases. These leases expire at various dates through 2029 and include discounted rental periods and fixed escalation clauses, which are amortized straight-line over the terms of the lease. Rent expense under operating leases was $10.6 million and $9.1 million in the three months ended September 30, 2017 and 2016 , respectively, and $33.3 million and $23.9 million in the nine months ended September 30, 2017 and 2016 , respectively. The Company has issued letters of credit for approximately $13.8 million and $10.6 million as security for these lease agreements as of September 30, 2017 and December 31, 2016 , respectively. As of December 31, 2016 , the future minimum rental commitments under non-cancelable leases with initial or remaining terms in excess of one year totaled $568.7 million . Subsequent to December 31, 2016 , the Company entered into additional non-cancelable leases in the United States ("U.S.") with initial or remaining terms in excess of one year with total future minimum lease commitments of $231.0 million . Future lease payments have not been reduced by minimum sublease rentals of $9.4 million due to the Company in the future under non-cancelable subleases through 2020 . The Company establishes assets and liabilities for the estimated construction costs incurred under lease arrangements where the Company is considered the owner for accounting purposes only, or build-to-suit leases, to the extent the Company is involved in the construction of structural improvements or takes construction risk prior to commencement of a lease. Upon occupancy of facilities under build-to-suit leases, the Company assesses whether these arrangements qualify for sales recognition under the sale-leaseback accounting guidance. If the Company continues to be the deemed owner, the facilities are accounted for as financing leases. The construction of one warehouse lease arrangement was completed during the three months ended June 30, 2016, and because the Company concluded it had a letter of credit of $1.2 million , the Company did not meet the sale-leaseback criteria for derecognition of the building asset and liability. The construction of a second warehouse lease arrangement was completed in the three months ended March 31, 2017, and because the Company concluded it had a letter of credit of $0.8 million , the Company did not meet the sale-leaseback criteria for derecognition of the building asset and liability. The construction of a third warehouse lease arrangement was completed in the three months ended June 30, 2017, and because the Company concluded it had a letter of credit of $1.0 million , the Company did not meet the sale-leaseback criteria for derecognition of the building asset and liability. Accordingly, these leases were accounted for as financing obligations and $28.9 million , $12.6 million , and $41.2 million was recorded in "Lease financing obligation" in the Company’s unaudited consolidated and condensed balance sheets as of June 30, 2016, March 31, 2017, and June 30, 2017, respectively. The monthly rent payments made to the lessor under the lease agreement are recorded in the Company’s financial statements as land lease expense and principal and interest on the financing obligation. Interest expense on the lease financing obligation reflects the portion of the Company's monthly lease payments that is allocated to interest expense. For the three and nine months ended September 30, 2017 , land lease expense was $0.2 million and $0.7 million , respectively, and interest expense on lease financing obligations was $2.0 million and $4.9 million , respectively. As of September 30, 2017 , future minimum commitments related to the financing obligations were $6.7 million and $39.0 million for principal and interest, respectively, through September 30, 2022. Collection of Sales or Other Similar Taxes In the U.S., Supreme Court decisions restrict states' rights to require remote sellers to collect state and local sales taxes (although some states are seeking to have the Supreme Court revisit these decisions). States have, and may again in the future, issued assessments and presented legal claims alleging that the Company is required to collect and remit sales or other similar taxes. The Company does not believe that it is obligated to collect and remit such taxes, and intends to vigorously defend its position. At this time, the Company believes any losses that may arise from these assessments and claims would be immaterial; however, no assurance can be given as to the outcomes and the Company could be subject to significant additional tax liabilities. Legal Matters In September 2016, a putative class action complaint was filed against the Company in the Superior Court of the province of Quebec (Naomi Zouzout v. Wayfair LLC, Case No. PQ 500-06-000809-166) by an individual on behalf of herself and on behalf of all other similarly situated individuals alleging violations of various Canadian consumer protection statutes. Among other remedies, this lawsuit seeks compensatory and punitive money damages, costs, and various fees. In June 2017, the Company entered into a settlement of the litigation, subject to judicial approval. The parties presented the settlement for review and approval by the court in September 2017. This settlement is not expected to have a material adverse effect on the Company's results of operation or financial condition. From time to time the Company is involved in claims that arise during the ordinary course of business. Although the results of litigation and claims cannot be predicted with certainty, the Company does not currently believe that the outcome of any of these other legal matters will have a material adverse effect on the Company's results of operation or financial condition. Regardless of the outcome, litigation can be costly and time consuming, as it can divert management's attention from important business matters and initiatives, negatively impacting the Company's overall operations. In addition, the Company may also find itself at greater risk to outside party claims as it increases its operations in jurisdictions where the laws with respect to the potential liability of online retailers are uncertain, unfavorable, or unclear.

Equity-Based Compensation

Equity-Based Compensation	9 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity-Based Compensation	Equity-Based Compensation The board of directors of the Company (the "Board") adopted the 2014 Incentive Award Plan ("2014 Plan") to grant cash and equity incentive awards to eligible participants in order to attract, motivate and retain talent. The 2014 Plan is administered by the Board with respect to awards to non-employee directors and by the compensation committee of the Board with respect to other participants and provides for the issuance of stock options, SARs, restricted stock, restricted stock units ("RSUs"), performance shares, stock payments, cash payments, dividend awards and other incentives. Prior to the adoption of the 2014 Plan, Wayfair LLC issued certain equity awards pursuant to the Wayfair LLC Amended and Restated Common Unit Plan (the “2010 Plan”), which was administered by the board of directors of Wayfair LLC. Awards issued under the 2010 Plan that remain outstanding currently represent Class A or Class B common stock of the Company. 8,603,066 shares of Class A common stock were initially available for issuance under awards granted pursuant to the 2014 Plan. The 2014 Plan also contains an evergreen provision whereby the shares available for future grant are increased on the first day of each calendar year beginning January 1, 2016 and ending on and including January 1, 2024. As of January 1, 2017, 8,389,750 shares of Class A common stock were available for future grant under the 2014 Plan. Shares or RSUs forfeited, withheld for minimum statutory tax obligations, and unexercised stock option lapses from the 2010 and 2014 Plans are available for grants of awards under the 2014 Plan. All equity awards granted prior to the initial public offering ("IPO") were subject to two vesting conditions: (i) a service period (typically five years ) and (ii) a performance condition (a liquidity event in the form of either a change of control or an IPO, each as defined in the 2010 Plan). Employees were able to retain provisionally vested stock options and shares upon departure. The Company determined that a liquidity event was not probable until the closing of its IPO on October 7, 2014, and as such, no expense was recognized until that date. After the IPO, pre-IPO awards for employees that continued providing service continued to vest over the remaining service period. 2014 Plan awards are expected to vest over the service period. The Company adopted Financial Accounting Standards Board ("FASB") Accounting Standards Update ("ASU") No. 2016-09, "Compensation - Stock Compensation" ("ASU 2016-09") as of January 1, 2017. For additional information, refer to Note 14, Recent Accounting Pronouncements . The following table presents activity relating to stock options for the nine months ended September 30, 2017 : Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (Years) Outstanding at December 31, 2016 209,759 $ 2.98 4.5 Options exercised (72,296 ) $ 2.92 Outstanding and exercisable at September 30, 2017 137,463 $ 3.01 3.7 Intrinsic value of stock options exercised was $4.1 million for the nine months ended September 30, 2017 . Aggregate intrinsic value of stock options outstanding and currently exercisable is $8.9 million . All stock options were fully vested at September 30, 2017 . The following table presents activity relating to restricted common stock for the nine months ended September 30, 2017 : Shares Weighted- Average Fair Value Outstanding at December 31, 2016 60,000 $ 35.05 Unvested at September 30, 2017 60,000 $ 67.40 Aggregate intrinsic value of restricted common stock unvested is $4.0 million as of September 30, 2017 . Unrecognized equity based compensation expense related to unvested restricted common stock is $2.7 million with a weighted average remaining vesting term of 1.3 years as of September 30, 2017 . The following table presents activity relating to RSUs for the nine months ended September 30, 2017 : Shares Weighted- Average Grant Date Fair Value Outstanding at December 31, 2016 6,986,776 $ 34.21 RSUs granted 2,271,235 $ 52.39 RSUs vested (1,766,511 ) $ 32.30 RSUs forfeited/canceled (1,117,090 ) $ 37.53 Outstanding at September 30, 2017 6,374,410 $ 41.04 The intrinsic value of RSUs vested was $99.3 million for the nine months ended September 30, 2017 . Aggregate intrinsic value of RSUs outstanding is $429.6 million as of September 30, 2017 . Unrecognized equity based compensation expense related to outstanding RSUs is $231.5 million with a weighted average remaining vesting term of 1.7 years at September 30, 2017 .

Segment and Geographic Informat

Segment and Geographic Information	9 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Segment and Geographic Information	Segment and Geographic Information Operating segments are defined as components of an enterprise for which separate financial information is available that is evaluated on a regular basis by the Chief Operating Decision Maker (“CODM”) in deciding how to allocate resources to an individual segment and in assessing performance. The Company’s CODM is its Chief Executive Officer. Beginning the fourth quarter of 2016, the Company changed its operating and reportable segments to U.S. and International. These segments reflect the way the CODM allocates resources and evaluates financial performance, which is based upon each segment's Adjusted EBITDA. Adjusted EBITDA is defined as loss before depreciation and amortization, equity-based compensation and related taxes, interest and other income and expense, provision for income taxes, and non-recurring items. These charges are excluded from evaluation of segment performance because it facilitates reportable segment performance comparisons on a period-to-period basis. Refer to Note 2, Summary of Significant Accounting Policies for the accounting policies of segments. The Company allocates certain operating expenses to the operating and reportable segments, including "Customer service and merchant fees," "Merchandising, marketing and sales," and "Operations, technology, general and administrative" based on the usage and relative contribution provided to the segments. It excludes from the allocations certain operating expense lines, including "Depreciation and amortization, "Equity based compensation and related taxes," "Interest (income), net," "Other (income) expense, net," and "Provision for income taxes." There are no revenue transactions between the Company's reportable segments. U.S. The U.S. segment primarily consists of amounts earned through product sales through the Company's sites in the U.S. and through sites operated by third parties in the U.S. International The International segment primarily consists of amounts earned through product sales through the Company's international sites. Revenue from external customers for each group of similar products and services are not reported to the CODM. Separate identification of this information for purposes of segment disclosure is impractical, as it is not readily available and the cost to develop it would be excessive. No individual country outside of the U.S. provided greater than 10% of total revenue. The following tables present Direct Retail and Other net revenues and Adjusted EBITDA attributable to the Company's reportable segments for the periods presented (in thousands): Three months ended September 30, Nine months ended September 30, 2017 2016 2017 2016 U.S. Direct Retail $ 1,033,669 $ 759,674 $ 2,847,898 $ 2,134,782 U.S. Other 16,975 28,127 57,843 91,613 U.S. segment net revenue 1,050,644 787,801 2,905,741 2,226,395 International Direct Retail 147,554 72,724 376,138 165,119 International Other — 1,000 — 4,287 International segment net revenue 147,554 73,724 376,138 169,406 Total net revenue $ 1,198,198 $ 861,525 $ 3,281,879 $ 2,395,801 Three months ended September 30, Nine months ended September 30, 2017 2016 2017 2016 Adjusted EBITDA U.S. $ 4,531 $ (7,857 ) $ 28,684 $ (11,816 ) International (27,203 ) (22,992 ) (74,498 ) (64,850 ) Total reportable segments Adjusted EBITDA (22,672 ) (30,849 ) (45,814 ) (76,666 ) Less: reconciling items (1) (53,757 ) (30,091 ) (126,029 ) (73,753 ) Net loss $ (76,429 ) $ (60,940 ) $ (171,843 ) $ (150,419 ) (1) Adjustments are made to reconcile total reportable segments Adjusted EBITDA to consolidated net loss including the following (in thousands): Three months ended September 30, Nine months ended September 30, 2017 2016 2017 2016 Depreciation and amortization (1) $ 22,913 $ 15,463 $ 62,588 $ 38,528 Equity based compensation and related taxes 19,598 15,308 50,539 37,265 Interest expense (income), net 2,008 292 3,857 (791 ) Other expense (income), net 227 (889 ) (400 ) (1,804 ) Provision for (benefit from) income taxes 237 (83 ) 671 555 Other (1) 8,774 — 8,774 — Total reconciling items $ 53,757 $ 30,091 $ 126,029 $ 73,753 (1) The Company recorded $9.6 million of one-time charges in the three and nine months ended September 30, 2017 in " Operations, technology, general and administrative " in the unaudited consolidated and condensed statements of operations related to a warehouse the Company vacated in July 2017. Of the $9.6 million charges, $8.8 million was included in "Other" and related primarily to the excess of the Company's estimated future remaining lease commitments through 2023 over its expected sublease income over the same period, and $0.8 million was included in "Depreciation and amortization" related to accelerated depreciation of leasehold improvements in the warehouse. The following table presents the activity related to the Company’s net revenue from Direct Retail sales derived through the Company’s sites and Other sales derived through sites operated by third parties and fees from third-party advertising distribution providers (in thousands): Three months ended September 30, Nine months ended September 30, 2017 2016 2017 2016 Net revenue Direct Retail $ 1,181,223 $ 832,398 $ 3,224,036 $ 2,299,901 Other 16,975 29,127 57,843 95,900 Net revenue $ 1,198,198 $ 861,525 $ 3,281,879 $ 2,395,801 The following table presents long-lived assets by segment (in thousands): September 30, December 31, Geographic long-lived assets U.S. $ 311,565 $ 233,099 International 7,308 6,255 Total $ 318,873 $ 239,354

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income tax expense (benefit) was $ 0.2 million and $ (0.1) million for the three months ended September 30, 2017 and 2016 , respectively, and $0.7 million and $0.6 million for the nine months ended September 30, 2017 and 2016 , respectively. The income tax expense recorded in the three and nine months ended September 30, 2017 and 2016 is primarily related to various foreign income tax assessments, state income taxes and to a lesser extent the amortization of goodwill for tax purposes for which there is no corresponding book deduction. Deferred income taxes reflect the impact of temporary differences between the amounts of assets and liabilities for financial reporting purposes and such amounts as measured by tax laws. The Company has deferred tax assets related to its net operating loss carryforwards accumulated since the fourth quarter of 2014 and related to net operating loss carryforwards of certain of its foreign subsidiaries. A valuation allowance against net deferred tax assets is required if, based upon the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company reassesses the valuation allowance on a quarterly basis and has provided a valuation allowance for the full amount of its net deferred tax assets. The Company had no unrecognized tax benefits as of September 30, 2017 and December 31, 2016 . The Company’s policy is to recognize interest and penalties related to unrecognized tax benefits as a component of income tax expense.

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit)	9 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Stockholders' Equity (Deficit)	Stockholders’ Equity (Deficit) Preferred Stock The Company authorized 10,000,000 shares of undesignated preferred stock, $0.001 par value per share, for future issuance. As of September 30, 2017 , the Company had no shares of undesignated preferred stock issued or outstanding. Common Stock The Company authorized 500,000,000 shares of Class A common stock, $0.001 par value per share, and 164,000,000 shares of Class B common stock, $0.001 par value per share, of which 56,355,606 and 49,945,202 shares of Class A common stock and 31,290,483 and 35,885,692 shares of Class B common stock were outstanding as of September 30, 2017 and December 31, 2016 , respectively. The rights of the holders of Class A common stock and Class B common stock are identical, except with respect to voting and conversion rights. Each share of Class A common stock is entitled to one vote per share and each share of Class B common stock is entitled to ten votes per share. Each share of Class B common stock may be converted into one share of Class A common stock at the option of its holder and will be automatically converted into one share of Class A common stock upon transfer thereof, subject to certain exceptions. In addition, upon the date on which the outstanding shares of Class B common stock represent less than 10% of the aggregate number of shares of the then outstanding Class A common stock and Class B common stock, or in the event of the affirmative vote or written consent of holders of at least 66 2/3% of the outstanding shares of Class B common stock, all outstanding shares of Class B common stock shall convert automatically into Class A common stock. Subject to preferences that may apply to any shares of preferred stock outstanding at the time, the holders of common stock are entitled to receive dividends out of funds legally available if the Board, in its discretion, determines to issue dividends and then only at the times and in the amounts that the Board may determine. Since the IPO through September 30, 2017 , 43,039,105 shares of Class B common stock were converted to Class A common stock.

Credit Agreement

Credit Agreement	9 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Credit Agreement	Credit Agreement On February 22, 2017, the Company entered into a $40 million credit card program and a credit agreement consisting of a $100 million secured revolving credit facility (the "Revolver") with Citibank, N.A. ("Citibank"). The Citibank credit facility replaced the Company's existing credit facility with Bank of America, N.A. ("Bank of America"), which was terminated on February 22, 2017 as described below. On September 11, 2017, the Citibank credit agreement was amended with a new letter of credit sublimit ( $25 million ) and to make clarifying edits to the mandatory prepayment provisions of the credit agreement. The Citibank Revolver has a $25 million letter of credit sublimit and a $10 million swing line sublimit, and a final maturity date of February 21, 2020. Wayfair LLC is the borrower (the "Borrower") under the Citibank credit agreement. Subject to certain conditions, the Borrower has the right to increase the Revolver by $25 million . Borrowings under the Revolver will bear interest through maturity at a variable rate based upon, at the Borrower’s option, either the Eurodollar rate or the base rate (which is the highest of (x) Citibank's prime rate, (y) one-half of 1.00% in excess of the federal funds effective rate, and (z) 1.00% in excess of the one-month Eurodollar rate), plus, in each case an applicable margin. From closing until September 30, 2019, the applicable margin for Eurodollar rate loans is 1.75% per annum and the applicable margin for base rate loans is 0.75% per annum. After September 30, 2019, the applicable margin is subject to specified changes depending on the applicable consolidated leverage ratio. Any amounts outstanding under the Revolver are due at maturity. In addition, subject to the terms and conditions set forth in the credit agreement, the Borrower is required to make certain mandatory prepayments prior to maturity. The Citibank credit agreement contains affirmative and negative covenants customarily applicable to senior secured credit facilities, including covenants that, among other things, will limit or restrict the ability of the Company and its subsidiaries, subject to negotiated exceptions, to incur additional indebtedness and additional liens on their assets, engage in mergers or acquisitions or dispose of assets, pay dividends or make other distributions, voluntarily prepay other indebtedness, enter into transactions with affiliated persons, make investments, and change the nature of their businesses. In addition, the Citibank credit agreement requires the Company to maintain certain financial ratios. As of September 30, 2017 , the Company was in compliance with its covenants under the Revolver. The Company previously had a credit agreement with Bank of America, which was replaced by the Citibank credit agreement on February 22, 2017. The Bank of America credit agreement provided the Company with a $20.0 million revolving line of credit to support direct borrowings and letters of credit, provided that a maximum of $5.0 million could be applied to direct borrowings under the revolving line of credit, plus an additional $45.0 million credit card program (which the Company continued to utilize on a transitional basis as of September 30, 2017), for a maximum aggregate commitment of $65.0 million . Subject to the terms and conditions of the Bank of America credit agreement, advances under the line of credit, if any, would bear interest at the LIBOR rate, plus 1.75% . The Bank of America credit agreement also required the Company to maintain certain covenants, including debt service coverage, tangible net worth and unencumbered liquid assets. The Company did not borrow any amounts under the Revolver or the Bank of America credit agreement during the nine months ended September 30, 2017 and the year ended December 31, 2016 . Convertible Debt On September 15, 2017, the Company issued $431.25 million aggregate principal amount of 0.375% Convertible Senior Notes due 2022 (the "Notes"), which includes the exercise in full of the $56.25 million over-allotment option, to Citigroup Global Markets Inc. and Goldman Sachs & Co. LLC as the initial purchasers of the Notes (the "Initial Purchasers"). The net proceeds from the sale of the Notes were approximately $420.4 million , after deducting the Initial Purchasers’ discounts and the estimated offering expenses payable by the Company. The Company used approximately $44.2 million of the net proceeds from the offering to pay the cost of the capped call transactions, as further described below, with three financial institutions (the "Option Counterparties"). The Company intends to use the remainder of the net proceeds for working capital and general corporate purposes. The Notes were issued pursuant to an indenture, dated September 15, 2017 (the "Indenture"), between the Company and U.S. Bank National Association, as trustee. The Company will pay interest on the Notes semiannually in arrears at a rate of 0.375% per annum on March 1 and September 1 of each year commencing on March 1, 2018. The Notes are convertible based upon an initial conversion rate of 9.61 shares of the Company’s Class A common stock per $1,000 principal amount of Notes (equivalent to a conversion price of approximately $104.06 per share of the Company’s Class A common stock). The conversion rate will be subject to adjustment upon the occurrence of certain specified events, including certain distributions and dividends to all or substantially all of the holders of the Company’s Class A common stock, but will not be adjusted for accrued and unpaid interest. The Company will settle any conversions of the Notes in cash, shares of the Company’s Class A common stock or a combination thereof, with the form of consideration determined at the Company’s election. The Notes will mature on September 1, 2022, unless earlier purchased, redeemed or converted. Prior to June 1, 2022, holders may convert all or a portion of their Notes only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on December 31, 2017 (and only during such calendar quarter), if the last reported sale price of the Company’s Class A common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; (2) during the five business day period after any ten consecutive trading day period (the "measurement period") in which the trading price per $1,000 principal amount of Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Company’s Class A common stock and the conversion rate on each such trading day; (3) with respect to any Notes called for redemption by the Company, at any time prior to the close of business on the second scheduled trading day immediately preceding the redemption date; or (4) upon the occurrence of specified corporate events. On and after June 1, 2022 until the close of business on the second scheduled trading day immediately preceding the maturity date, holders may convert their Notes at any time, regardless of the foregoing circumstances. Holders of Notes who convert their Notes in connection with a make-whole fundamental change or a notice of redemption (each as defined in the Indenture) may be entitled to a premium in the form of an increase in the conversion rate of the Notes. The Company may not redeem the Notes prior to September 8, 2020. On or after September 8, 2020, the Company may redeem for cash all or part of the Notes if the last reported sale price of the Company’s Class A common stock equals or exceeds 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive), including at least one of the five trading days immediately preceding the date on which the Company provides notice of redemption, during any 30 consecutive trading days ending on, and including the trading day immediately preceding the date on which the Company provides notice of the redemption. The redemption price will be 100% of the principal amount of the Notes to be redeemed, plus accrued and unpaid interest, if any. Upon the occurrence of a fundamental change (as defined in the Indenture), holders may require the Company to repurchase all or a portion of their Notes for cash at a price equal to 100% of the principal amount of the Notes to be repurchased plus any accrued but unpaid interest to, but excluding, the fundamental change repurchase date. The Indenture contains customary terms and covenants, including that upon certain events of default occurring and continuing, either the Trustee or the holders of not less than 25% in aggregate principal amount of the Notes then outstanding may declare the entire principal amount of all the Notes plus accrued interest, if any, to be immediately due and payable. The Notes are general unsecured obligations of the Company. The Notes rank senior in right of payment to any of the Company’s future indebtedness that is expressly subordinated in right of payment to the Notes; rank equal in right of payment to the Company’s existing and future unsecured indebtedness that is not so subordinated; are effectively subordinated in right of payment to any of the Company’s secured indebtedness to the extent of the value of the assets securing such indebtedness; and are structurally subordinated to all existing and future indebtedness and liabilities of the Company’s subsidiaries. In accounting for the issuance of the Notes, the Company separated the Notes into liability and equity components. The carrying amount of the liability component was calculated by measuring the fair value of a similar liability that does not have an associated convertible feature. The carrying amount of the equity component, representing the conversion option, was determined by deducting the fair value of the liability component from the par value of the Notes. The difference between the principal amount of the Notes and the liability component represents the debt discount, which is recorded as a direct deduction from the related debt liability in the consolidated and condensed balance sheet and amortized to interest expense using the effective interest method over the term of the Notes. The equity component of the Notes of approximately $95.8 million is included in additional paid-in capital in the consolidated and condensed balance sheet and is not remeasured as long as it continues to meet the conditions for equity classification. The Company allocated transaction costs related to the Notes using the same proportions as the proceeds from the Notes. Transaction costs attributable to the liability component were recorded as a direct deduction from the related debt liability in the consolidated and condensed balance sheet and amortized to interest expense over the term of the Notes, and transaction costs attributable to the equity component were netted with the equity component in shareholders’ equity. Interest expense related to the Notes for the three and nine months ended September 30, 2017 was $0.9 million and $0.9 million , respectively, which is also comprised of the amortization of debt discount and debt issuance costs and the contractual coupon interest. Accrued interest related to the Notes as of September 30, 2017 was $0.9 million and is recorded in " Accrued expenses " in the unaudited consolidated and condensed balance sheet. The estimated fair value of the Notes was $415.0 million as of September 30, 2017. The estimated fair value of the Notes was determined through consideration of quoted market prices. The fair value is classified as Level 2, as defined in Note 3, Marketable Securities and Fair Value Measurements . On September 11, 2017, the Company entered into privately negotiated capped call transactions (the "Base Capped Call Transactions") with the Option Counterparties and, in connection with the exercise in full of the over-allotment option by the Initial Purchasers, on September 14, 2017 entered into additional capped call transactions (such additional capped call transactions, the "Additional Capped Call Transactions" and, together with the Base Capped Call Transactions, the "Capped Call Transactions") with the Option Counterparties. The Capped Call Transactions are expected generally to reduce the potential dilution and/or offset the cash payments the Company is required to make in excess of the principal amount of the Notes upon conversion of the Notes in the event that the market price per share of the Company’s Class A common stock is greater than the strike price of the Capped Call Transactions (which initially corresponds to the initial conversion price of the Notes and is subject to certain adjustments under the terms of the Capped Call Transactions), with such reduction and/or offset subject to a cap based on the cap price of the Capped Call Transactions. The Capped Call Transactions have an initial cap price of $154.16 per share of the Company’s Class A common stock, which represents a premium of 100% over the last reported sale price of the Company’s Class A common stock on September 11, 2017, and is subject to certain adjustments under the terms of the Capped Call Transactions. Collectively, the Capped Call Transactions cover, initially, the number of shares of the Company’s Class A common stock underlying the Notes, subject to anti-dilution adjustments substantially similar to those applicable to the Notes. The Capped Call Transactions are separate transactions, in each case, entered into by the Company with the Option Counterparties, and are not part of the terms of the Notes and will not affect any holder’s rights under the Notes. Holders of the Notes will not have any rights with respect to the Capped Call Transactions. The Capped Call Transactions do not meet the criteria for separate accounting as a derivative as they are indexed to the Company's stock. The premiums paid for the Capped Call Transactions have been included as a net reduction to additional paid-in capital within shareholders’ equity.

Convertible Debt

Convertible Debt	9 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Convertible Debt	Credit Agreement On February 22, 2017, the Company entered into a $40 million credit card program and a credit agreement consisting of a $100 million secured revolving credit facility (the "Revolver") with Citibank, N.A. ("Citibank"). The Citibank credit facility replaced the Company's existing credit facility with Bank of America, N.A. ("Bank of America"), which was terminated on February 22, 2017 as described below. On September 11, 2017, the Citibank credit agreement was amended with a new letter of credit sublimit ( $25 million ) and to make clarifying edits to the mandatory prepayment provisions of the credit agreement. The Citibank Revolver has a $25 million letter of credit sublimit and a $10 million swing line sublimit, and a final maturity date of February 21, 2020. Wayfair LLC is the borrower (the "Borrower") under the Citibank credit agreement. Subject to certain conditions, the Borrower has the right to increase the Revolver by $25 million . Borrowings under the Revolver will bear interest through maturity at a variable rate based upon, at the Borrower’s option, either the Eurodollar rate or the base rate (which is the highest of (x) Citibank's prime rate, (y) one-half of 1.00% in excess of the federal funds effective rate, and (z) 1.00% in excess of the one-month Eurodollar rate), plus, in each case an applicable margin. From closing until September 30, 2019, the applicable margin for Eurodollar rate loans is 1.75% per annum and the applicable margin for base rate loans is 0.75% per annum. After September 30, 2019, the applicable margin is subject to specified changes depending on the applicable consolidated leverage ratio. Any amounts outstanding under the Revolver are due at maturity. In addition, subject to the terms and conditions set forth in the credit agreement, the Borrower is required to make certain mandatory prepayments prior to maturity. The Citibank credit agreement contains affirmative and negative covenants customarily applicable to senior secured credit facilities, including covenants that, among other things, will limit or restrict the ability of the Company and its subsidiaries, subject to negotiated exceptions, to incur additional indebtedness and additional liens on their assets, engage in mergers or acquisitions or dispose of assets, pay dividends or make other distributions, voluntarily prepay other indebtedness, enter into transactions with affiliated persons, make investments, and change the nature of their businesses. In addition, the Citibank credit agreement requires the Company to maintain certain financial ratios. As of September 30, 2017 , the Company was in compliance with its covenants under the Revolver. The Company previously had a credit agreement with Bank of America, which was replaced by the Citibank credit agreement on February 22, 2017. The Bank of America credit agreement provided the Company with a $20.0 million revolving line of credit to support direct borrowings and letters of credit, provided that a maximum of $5.0 million could be applied to direct borrowings under the revolving line of credit, plus an additional $45.0 million credit card program (which the Company continued to utilize on a transitional basis as of September 30, 2017), for a maximum aggregate commitment of $65.0 million . Subject to the terms and conditions of the Bank of America credit agreement, advances under the line of credit, if any, would bear interest at the LIBOR rate, plus 1.75% . The Bank of America credit agreement also required the Company to maintain certain covenants, including debt service coverage, tangible net worth and unencumbered liquid assets. The Company did not borrow any amounts under the Revolver or the Bank of America credit agreement during the nine months ended September 30, 2017 and the year ended December 31, 2016 . Convertible Debt On September 15, 2017, the Company issued $431.25 million aggregate principal amount of 0.375% Convertible Senior Notes due 2022 (the "Notes"), which includes the exercise in full of the $56.25 million over-allotment option, to Citigroup Global Markets Inc. and Goldman Sachs & Co. LLC as the initial purchasers of the Notes (the "Initial Purchasers"). The net proceeds from the sale of the Notes were approximately $420.4 million , after deducting the Initial Purchasers’ discounts and the estimated offering expenses payable by the Company. The Company used approximately $44.2 million of the net proceeds from the offering to pay the cost of the capped call transactions, as further described below, with three financial institutions (the "Option Counterparties"). The Company intends to use the remainder of the net proceeds for working capital and general corporate purposes. The Notes were issued pursuant to an indenture, dated September 15, 2017 (the "Indenture"), between the Company and U.S. Bank National Association, as trustee. The Company will pay interest on the Notes semiannually in arrears at a rate of 0.375% per annum on March 1 and September 1 of each year commencing on March 1, 2018. The Notes are convertible based upon an initial conversion rate of 9.61 shares of the Company’s Class A common stock per $1,000 principal amount of Notes (equivalent to a conversion price of approximately $104.06 per share of the Company’s Class A common stock). The conversion rate will be subject to adjustment upon the occurrence of certain specified events, including certain distributions and dividends to all or substantially all of the holders of the Company’s Class A common stock, but will not be adjusted for accrued and unpaid interest. The Company will settle any conversions of the Notes in cash, shares of the Company’s Class A common stock or a combination thereof, with the form of consideration determined at the Company’s election. The Notes will mature on September 1, 2022, unless earlier purchased, redeemed or converted. Prior to June 1, 2022, holders may convert all or a portion of their Notes only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on December 31, 2017 (and only during such calendar quarter), if the last reported sale price of the Company’s Class A common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; (2) during the five business day period after any ten consecutive trading day period (the "measurement period") in which the trading price per $1,000 principal amount of Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Company’s Class A common stock and the conversion rate on each such trading day; (3) with respect to any Notes called for redemption by the Company, at any time prior to the close of business on the second scheduled trading day immediately preceding the redemption date; or (4) upon the occurrence of specified corporate events. On and after June 1, 2022 until the close of business on the second scheduled trading day immediately preceding the maturity date, holders may convert their Notes at any time, regardless of the foregoing circumstances. Holders of Notes who convert their Notes in connection with a make-whole fundamental change or a notice of redemption (each as defined in the Indenture) may be entitled to a premium in the form of an increase in the conversion rate of the Notes. The Company may not redeem the Notes prior to September 8, 2020. On or after September 8, 2020, the Company may redeem for cash all or part of the Notes if the last reported sale price of the Company’s Class A common stock equals or exceeds 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive), including at least one of the five trading days immediately preceding the date on which the Company provides notice of redemption, during any 30 consecutive trading days ending on, and including the trading day immediately preceding the date on which the Company provides notice of the redemption. The redemption price will be 100% of the principal amount of the Notes to be redeemed, plus accrued and unpaid interest, if any. Upon the occurrence of a fundamental change (as defined in the Indenture), holders may require the Company to repurchase all or a portion of their Notes for cash at a price equal to 100% of the principal amount of the Notes to be repurchased plus any accrued but unpaid interest to, but excluding, the fundamental change repurchase date. The Indenture contains customary terms and covenants, including that upon certain events of default occurring and continuing, either the Trustee or the holders of not less than 25% in aggregate principal amount of the Notes then outstanding may declare the entire principal amount of all the Notes plus accrued interest, if any, to be immediately due and payable. The Notes are general unsecured obligations of the Company. The Notes rank senior in right of payment to any of the Company’s future indebtedness that is expressly subordinated in right of payment to the Notes; rank equal in right of payment to the Company’s existing and future unsecured indebtedness that is not so subordinated; are effectively subordinated in right of payment to any of the Company’s secured indebtedness to the extent of the value of the assets securing such indebtedness; and are structurally subordinated to all existing and future indebtedness and liabilities of the Company’s subsidiaries. In accounting for the issuance of the Notes, the Company separated the Notes into liability and equity components. The carrying amount of the liability component was calculated by measuring the fair value of a similar liability that does not have an associated convertible feature. The carrying amount of the equity component, representing the conversion option, was determined by deducting the fair value of the liability component from the par value of the Notes. The difference between the principal amount of the Notes and the liability component represents the debt discount, which is recorded as a direct deduction from the related debt liability in the consolidated and condensed balance sheet and amortized to interest expense using the effective interest method over the term of the Notes. The equity component of the Notes of approximately $95.8 million is included in additional paid-in capital in the consolidated and condensed balance sheet and is not remeasured as long as it continues to meet the conditions for equity classification. The Company allocated transaction costs related to the Notes using the same proportions as the proceeds from the Notes. Transaction costs attributable to the liability component were recorded as a direct deduction from the related debt liability in the consolidated and condensed balance sheet and amortized to interest expense over the term of the Notes, and transaction costs attributable to the equity component were netted with the equity component in shareholders’ equity. Interest expense related to the Notes for the three and nine months ended September 30, 2017 was $0.9 million and $0.9 million , respectively, which is also comprised of the amortization of debt discount and debt issuance costs and the contractual coupon interest. Accrued interest related to the Notes as of September 30, 2017 was $0.9 million and is recorded in " Accrued expenses " in the unaudited consolidated and condensed balance sheet. The estimated fair value of the Notes was $415.0 million as of September 30, 2017. The estimated fair value of the Notes was determined through consideration of quoted market prices. The fair value is classified as Level 2, as defined in Note 3, Marketable Securities and Fair Value Measurements . On September 11, 2017, the Company entered into privately negotiated capped call transactions (the "Base Capped Call Transactions") with the Option Counterparties and, in connection with the exercise in full of the over-allotment option by the Initial Purchasers, on September 14, 2017 entered into additional capped call transactions (such additional capped call transactions, the "Additional Capped Call Transactions" and, together with the Base Capped Call Transactions, the "Capped Call Transactions") with the Option Counterparties. The Capped Call Transactions are expected generally to reduce the potential dilution and/or offset the cash payments the Company is required to make in excess of the principal amount of the Notes upon conversion of the Notes in the event that the market price per share of the Company’s Class A common stock is greater than the strike price of the Capped Call Transactions (which initially corresponds to the initial conversion price of the Notes and is subject to certain adjustments under the terms of the Capped Call Transactions), with such reduction and/or offset subject to a cap based on the cap price of the Capped Call Transactions. The Capped Call Transactions have an initial cap price of $154.16 per share of the Company’s Class A common stock, which represents a premium of 100% over the last reported sale price of the Company’s Class A common stock on September 11, 2017, and is subject to certain adjustments under the terms of the Capped Call Transactions. Collectively, the Capped Call Transactions cover, initially, the number of shares of the Company’s Class A common stock underlying the Notes, subject to anti-dilution adjustments substantially similar to those applicable to the Notes. The Capped Call Transactions are separate transactions, in each case, entered into by the Company with the Option Counterparties, and are not part of the terms of the Notes and will not affect any holder’s rights under the Notes. Holders of the Notes will not have any rights with respect to the Capped Call Transactions. The Capped Call Transactions do not meet the criteria for separate accounting as a derivative as they are indexed to the Company's stock. The premiums paid for the Capped Call Transactions have been included as a net reduction to additional paid-in capital within shareholders’ equity.

Net Loss per Share

Net Loss per Share	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss per Share Basic and diluted net loss per share is presented using the two class method required for participating securities: Class A and Class B common stock. The rights of the holders of Class A and Class B common stock are identical, except with respect to voting and conversion. For more information on the rights of Class A and Class B common stockholders, see Note 10, Stockholders' Equity (Deficit) . Basic net loss per share attributable to common stockholders is computed using the weighted-average number of shares of common stock outstanding during the period. Diluted net loss per share attributable to common stockholders is computed using the weighted-average number of shares of common stock and, if dilutive, common stock equivalents outstanding during the period. The Company's common stock equivalents consist of shares issuable upon the release of restricted stock units and unvested restricted stock, the exercise of stock options and potential shares from instruments convertible into common stock. The dilutive effect of these common stock equivalents is reflected in diluted earnings per share by application of the treasury stock method. The Company's basic and diluted net loss per share are the same because the Company has generated net loss attributable to common stockholders and common stock equivalents are excluded from diluted net loss per share because they have an antidilutive impact. The Company allocates undistributed earnings between the classes on a one -to- one basis when computing net loss per share. As a result, basic and diluted net loss per Class A and Class B shares are equivalent. The following table presents the calculation of basic and diluted net loss per share (in thousands, except per share data): Three months ended September 30, Nine months ended September 30, 2017 2016 2017 2016 Net loss $ (76,429 ) $ (60,940 ) $ (171,843 ) $ (150,419 ) Weighted average common shares used for basic and diluted net loss per share computation 87,283 85,105 86,679 84,779 Net loss per share: Basic and Diluted $ (0.88 ) $ (0.72 ) $ (1.98 ) $ (1.77 ) Dilutive common stock equivalents, representing potentially dilutive common stock options, restricted stock and restricted stock units, of 6.6 million for the three and nine months ended September 30, 2017 and 6.8 million for the three and nine months ended September 30, 2016 , were excluded from diluted earnings per share calculations for these periods because of their anti-dilutive effect. For the three and nine month periods ended September 30, 2017 , the Company also excluded the potentially dilutive impact to Class A shares from the issuance of the Notes, since their effect would have been anti-dilutive. The Capped Call Transactions are designed to reduce potential dilution of our Class A shares upon conversion of the Notes. For more information on the Notes and the Capped Call Transactions, see Note 12, Convertible Debt .

Recent Accounting Pronouncement

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2017
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements Stock Compensation In March 2016, the FASB issued ASU No. 2016-09, "Compensation - Stock Compensation" ("ASU 2016-09"). This ASU revises the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and an option to recognize gross stock compensation expense with actual forfeitures recognized as they occur, as well as certain classifications on the statement of cash flows. This ASU is effective for annual reporting periods beginning after December 15, 2016, including interim reporting periods within that reporting year, and early adoption is permitted. The Company adopted ASU 2016-09 as of January 1, 2017 using a modified retrospective approach with the option to recognize gross stock compensation expense with actual forfeitures recognized as they occur, with a cumulative-effect adjustment to retained earnings recognized as of January 1, 2017 of $8.7 million . The adoption of ASU 2016-09 also requires all income tax adjustments to be recorded in the consolidated and condensed statements of operations. Revenue Recognition In May 2014, the FASB issued ASU No. 2014-09, "Revenue from Contracts with Customers" ("ASU 2014-09"). This ASU is a comprehensive new revenue recognition model that requires a company to recognize revenue to depict the transfer of goods or services to a customer at an amount that reflects the consideration it expects to receive in exchange for those goods or services. This ASU was originally effective for annual reporting periods beginning after December 15, 2016 and early adoption was not permitted. In August 2015, the FASB issued ASU No. 2015-14, "Revenue from Contracts with Customers – Deferral of the Effective Date" (ASU-2015-14), which defers the effective date of ASU 2014-09 for one year and permits early adoption as early as the original effective date of ASU 2014-09. Accordingly, ASU 2014-09 is now effective for annual reporting periods beginning after December 15, 2017 and early adoption is permitted only as of annual reporting periods beginning after December 15, 2016, including interim reporting periods within that reporting year. In March 2016, the FASB issued ASU No. 2016-08, "Revenue from Contracts with Customers - Principal versus Agent Considerations" ("ASU 2016-08"). This ASU clarifies the implementation guidance for principal versus agent considerations in ASU 2014-09. This ASU is effective at the same period as ASU 2015-14 and ASU 2014-09. Management expects to adopt ASU 2014-09, ASU 2015-14, and ASU 2016-08 (collectively, the "Revenue Recognition Accounting Pronouncements") for annual reporting periods beginning after December 15, 2017, including interim reporting periods within that reporting year. While management is still in its assessment process, management generally expects to identify substantially similar performance obligations after adoption of the Revenue Recognition Accounting Pronouncements as compared with deliverables and separate units of accounting under previous revenue recognition guidance. Therefore, the Company generally does not expect the impact of the adoption of the Revenue Recognition Accounting Pronouncements to be significant to its consolidated financial statements, processes, or systems. As we continue to evaluate the impact of the Revenue Recognition Accounting Pronouncements, we have identified no material changes to our current revenue recognition accounting policy for product sales generated through the Company's sites, or Direct Retail, which we identified as our most significant revenue stream. Management expects to apply the Revenue Recognition Accounting Pronouncements retrospectively with the cumulative effect of initially applying the Revenue Recognition Accounting Pronouncements recognized at the date of initial application recorded as an adjustment to retained earnings, referred to as the "Modified Retrospective Approach." Leases In February 2016, the FASB issued ASU No. 2016-02, "Leases" ("ASU 2016-02"). This ASU revises the accounting related to leases by requiring lessees to recognize a lease liability and a right-of-use asset for all leases. The new lease guidance also simplifies the accounting for sale and leaseback transactions. This ASU is effective for annual reporting periods beginning after December 15, 2018 and early adoption is permitted. Management expects to adopt ASU 2016-02 for annual reporting periods beginning after December 15, 2018. Management is currently evaluating the impact of the adoption of this ASU on the Company’s consolidated financial statements, and expects it will have a material impact on our consolidated financial statements, primarily the consolidated balance sheets and related disclosures.

Recent Accounting Pronounceme21

Recent Accounting Pronouncements (Policies)	9 Months Ended
	Sep. 30, 2017
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements Stock Compensation In March 2016, the FASB issued ASU No. 2016-09, "Compensation - Stock Compensation" ("ASU 2016-09"). This ASU revises the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and an option to recognize gross stock compensation expense with actual forfeitures recognized as they occur, as well as certain classifications on the statement of cash flows. This ASU is effective for annual reporting periods beginning after December 15, 2016, including interim reporting periods within that reporting year, and early adoption is permitted. The Company adopted ASU 2016-09 as of January 1, 2017 using a modified retrospective approach with the option to recognize gross stock compensation expense with actual forfeitures recognized as they occur, with a cumulative-effect adjustment to retained earnings recognized as of January 1, 2017 of $8.7 million . The adoption of ASU 2016-09 also requires all income tax adjustments to be recorded in the consolidated and condensed statements of operations. Revenue Recognition In May 2014, the FASB issued ASU No. 2014-09, "Revenue from Contracts with Customers" ("ASU 2014-09"). This ASU is a comprehensive new revenue recognition model that requires a company to recognize revenue to depict the transfer of goods or services to a customer at an amount that reflects the consideration it expects to receive in exchange for those goods or services. This ASU was originally effective for annual reporting periods beginning after December 15, 2016 and early adoption was not permitted. In August 2015, the FASB issued ASU No. 2015-14, "Revenue from Contracts with Customers – Deferral of the Effective Date" (ASU-2015-14), which defers the effective date of ASU 2014-09 for one year and permits early adoption as early as the original effective date of ASU 2014-09. Accordingly, ASU 2014-09 is now effective for annual reporting periods beginning after December 15, 2017 and early adoption is permitted only as of annual reporting periods beginning after December 15, 2016, including interim reporting periods within that reporting year. In March 2016, the FASB issued ASU No. 2016-08, "Revenue from Contracts with Customers - Principal versus Agent Considerations" ("ASU 2016-08"). This ASU clarifies the implementation guidance for principal versus agent considerations in ASU 2014-09. This ASU is effective at the same period as ASU 2015-14 and ASU 2014-09. Management expects to adopt ASU 2014-09, ASU 2015-14, and ASU 2016-08 (collectively, the "Revenue Recognition Accounting Pronouncements") for annual reporting periods beginning after December 15, 2017, including interim reporting periods within that reporting year. While management is still in its assessment process, management generally expects to identify substantially similar performance obligations after adoption of the Revenue Recognition Accounting Pronouncements as compared with deliverables and separate units of accounting under previous revenue recognition guidance. Therefore, the Company generally does not expect the impact of the adoption of the Revenue Recognition Accounting Pronouncements to be significant to its consolidated financial statements, processes, or systems. As we continue to evaluate the impact of the Revenue Recognition Accounting Pronouncements, we have identified no material changes to our current revenue recognition accounting policy for product sales generated through the Company's sites, or Direct Retail, which we identified as our most significant revenue stream. Management expects to apply the Revenue Recognition Accounting Pronouncements retrospectively with the cumulative effect of initially applying the Revenue Recognition Accounting Pronouncements recognized at the date of initial application recorded as an adjustment to retained earnings, referred to as the "Modified Retrospective Approach." Leases In February 2016, the FASB issued ASU No. 2016-02, "Leases" ("ASU 2016-02"). This ASU revises the accounting related to leases by requiring lessees to recognize a lease liability and a right-of-use asset for all leases. The new lease guidance also simplifies the accounting for sale and leaseback transactions. This ASU is effective for annual reporting periods beginning after December 15, 2018 and early adoption is permitted. Management expects to adopt ASU 2016-02 for annual reporting periods beginning after December 15, 2018. Management is currently evaluating the impact of the adoption of this ASU on the Company’s consolidated financial statements, and expects it will have a material impact on our consolidated financial statements, primarily the consolidated balance sheets and related disclosures.

Marketable Securities and Fai22

Marketable Securities and Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Schedule of Marketable Securities	The following tables present details of the Company’s marketable securities as of September 30, 2017 and December 31, 2016 (in thousands): September 30, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Short-term: Investment securities $ 56,719 $ 12 $ (32 ) $ 56,699 Long-term: Investment securities 29,837 22 (50 ) 29,809 Total $ 86,556 $ 34 $ (82 ) $ 86,508 December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Short-term: Investment securities $ 63,135 $ 7 $ (39 ) $ 63,103 Commercial paper 5,641 1 (2 ) 5,640 Long-term: Investment securities 30,985 16 (34 ) 30,967 Total $ 99,761 $ 24 $ (75 ) $ 99,710
Schedule of the Fair Value of the Company's Financial Assets Measured at Fair Value on a Recurring Basis Based on the Three-Tier Value Hierarchy	The following tables set forth the fair value of the Company’s financial assets measured at fair value on a recurring basis as of September 30, 2017 and December 31, 2016 based on the three-tier value hierarchy (in thousands): September 30, 2017 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds and other funds $ 512,929 $ — $ — $ 512,929 Short-term investments: Investment securities — 56,699 — 56,699 Restricted cash: Certificate of deposit 5,000 — — 5,000 Long-term: Investment securities — 29,809 — 29,809 Total $ 517,929 $ 86,508 $ — $ 604,437 December 31, 2016 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 200,867 $ — $ — $ 200,867 Short-term investments: Investment securities — 63,103 — 63,103 Commercial paper — 5,640 — 5,640 Restricted cash: Certificate of deposit 5,000 — — 5,000 Long-term: Investment securities — 30,967 — 30,967 Total $ 205,867 $ 99,710 $ — $ 305,577

Intangible Assets and Goodwill

Intangible Assets and Goodwill (Tables)	9 Months Ended
	Sep. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets	The following table summarizes intangible assets as of September 30, 2017 and December 31, 2016 (in thousands): Weighted - Average Amortization Period (Years) September 30, 2017 Gross Carrying Amount Accumulated Amortization Net Book Value Trademarks 5 $ 1,900 $ (1,583 ) $ 317 Technology 3 1,453 (525 ) 928 Customer relationships 5 1,300 (1,083 ) 217 Total $ 4,653 $ (3,191 ) $ 1,462 Weighted - Average Amortization Period (Years) December 31, 2016 Gross Carrying Amount Accumulated Amortization Net Book Value Trademarks 5 $ 1,900 $ (1,298 ) $ 602 Technology 3 1,453 (161 ) 1,292 Customer relationship 5 1,300 (888 ) 412 Total $ 4,653 $ (2,347 ) $ 2,306

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	9 Months Ended
	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net	The following table summarizes property and equipment, net as of September 30, 2017 and December 31, 2016 (in thousands): September 30, December 31, Furniture and computer equipment $ 198,903 $ 133,297 Site and software development costs 108,456 77,429 Leasehold improvements 80,512 62,090 Construction in progress 10,416 47,013 Buildings (leased - Note 6) 83,681 29,856 481,968 349,685 Less accumulated depreciation and amortization (163,095 ) (110,331 ) Property and equipment, net $ 318,873 $ 239,354

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Activity Relating to Stock Options	The following table presents activity relating to stock options for the nine months ended September 30, 2017 : Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (Years) Outstanding at December 31, 2016 209,759 $ 2.98 4.5 Options exercised (72,296 ) $ 2.92 Outstanding and exercisable at September 30, 2017 137,463 $ 3.01 3.7
Summary of Activity Relating to Restricted Stock	The following table presents activity relating to RSUs for the nine months ended September 30, 2017 : Shares Weighted- Average Grant Date Fair Value Outstanding at December 31, 2016 6,986,776 $ 34.21 RSUs granted 2,271,235 $ 52.39 RSUs vested (1,766,511 ) $ 32.30 RSUs forfeited/canceled (1,117,090 ) $ 37.53 Outstanding at September 30, 2017 6,374,410 $ 41.04 The following table presents activity relating to restricted common stock for the nine months ended September 30, 2017 : Shares Weighted- Average Fair Value Outstanding at December 31, 2016 60,000 $ 35.05 Unvested at September 30, 2017 60,000 $ 67.40

Segment and Geographic Inform26

Segment and Geographic Information (Tables)	9 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Activity Related to Net Revenue, Adjusted EBITDA and Long-Lived Assets by Segment	The following tables present Direct Retail and Other net revenues and Adjusted EBITDA attributable to the Company's reportable segments for the periods presented (in thousands): Three months ended September 30, Nine months ended September 30, 2017 2016 2017 2016 U.S. Direct Retail $ 1,033,669 $ 759,674 $ 2,847,898 $ 2,134,782 U.S. Other 16,975 28,127 57,843 91,613 U.S. segment net revenue 1,050,644 787,801 2,905,741 2,226,395 International Direct Retail 147,554 72,724 376,138 165,119 International Other — 1,000 — 4,287 International segment net revenue 147,554 73,724 376,138 169,406 Total net revenue $ 1,198,198 $ 861,525 $ 3,281,879 $ 2,395,801 Three months ended September 30, Nine months ended September 30, 2017 2016 2017 2016 Adjusted EBITDA U.S. $ 4,531 $ (7,857 ) $ 28,684 $ (11,816 ) International (27,203 ) (22,992 ) (74,498 ) (64,850 ) Total reportable segments Adjusted EBITDA (22,672 ) (30,849 ) (45,814 ) (76,666 ) Less: reconciling items (1) (53,757 ) (30,091 ) (126,029 ) (73,753 ) Net loss $ (76,429 ) $ (60,940 ) $ (171,843 ) $ (150,419 ) (1) Adjustments are made to reconcile total reportable segments Adjusted EBITDA to consolidated net loss including the following (in thousands): Three months ended September 30, Nine months ended September 30, 2017 2016 2017 2016 Depreciation and amortization (1) $ 22,913 $ 15,463 $ 62,588 $ 38,528 Equity based compensation and related taxes 19,598 15,308 50,539 37,265 Interest expense (income), net 2,008 292 3,857 (791 ) Other expense (income), net 227 (889 ) (400 ) (1,804 ) Provision for (benefit from) income taxes 237 (83 ) 671 555 Other (1) 8,774 — 8,774 — Total reconciling items $ 53,757 $ 30,091 $ 126,029 $ 73,753 (1) The Company recorded $9.6 million of one-time charges in the three and nine months ended September 30, 2017 in " Operations, technology, general and administrative " in the unaudited consolidated and condensed statements of operations related to a warehouse the Company vacated in July 2017. Of the $9.6 million charges, $8.8 million was included in "Other" and related primarily to the excess of the Company's estimated future remaining lease commitments through 2023 over its expected sublease income over the same period, and $0.8 million was included in "Depreciation and amortization" related to accelerated depreciation of leasehold improvements in the warehouse. The following table presents the activity related to the Company’s net revenue from Direct Retail sales derived through the Company’s sites and Other sales derived through sites operated by third parties and fees from third-party advertising distribution providers (in thousands): Three months ended September 30, Nine months ended September 30, 2017 2016 2017 2016 Net revenue Direct Retail $ 1,181,223 $ 832,398 $ 3,224,036 $ 2,299,901 Other 16,975 29,127 57,843 95,900 Net revenue $ 1,198,198 $ 861,525 $ 3,281,879 $ 2,395,801 The following table presents long-lived assets by segment (in thousands): September 30, December 31, Geographic long-lived assets U.S. $ 311,565 $ 233,099 International 7,308 6,255 Total $ 318,873 $ 239,354

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Schedule of Calculation of Basic and Diluted Net Loss Per Share	The following table presents the calculation of basic and diluted net loss per share (in thousands, except per share data): Three months ended September 30, Nine months ended September 30, 2017 2016 2017 2016 Net loss $ (76,429 ) $ (60,940 ) $ (171,843 ) $ (150,419 ) Weighted average common shares used for basic and diluted net loss per share computation 87,283 85,105 86,679 84,779 Net loss per share: Basic and Diluted $ (0.88 ) $ (0.72 ) $ (1.98 ) $ (1.77 )

Basis of Presentation (Details)

Basis of Presentation (Details) supplier in Thousands, product in Millions	9 Months Ended
	Sep. 30, 2017productsupplier
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of products offered (more than) | product	8
Number of suppliers providing products offered (more than) | supplier	10

Marketable Securities and Fai29

Marketable Securities and Fair Value Measurements - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Estimated fair values	$ 86,508,000		$ 86,508,000		$ 99,710,000
Other-than-temporary impairment loss	0	$ 0	0	$ 0
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities, realized gains and losses	0	$ 0	0	$ 0
Long-term marketable securities
Fair Value Disclosures [Abstract]
Estimated fair values	$ 29,809,000		$ 29,809,000		$ 30,967,000
Long-term marketable securities | Minimum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities term			1 year
Long-term marketable securities | Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities term			3 years

Marketable Securities and Fai30

Marketable Securities and Fair Value Measurements - Schedule of Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Marketable securities and fair value measurements
Amortized Cost	$ 86,556	$ 99,761
Gross Unrealized Gains	34	24
Gross Unrealized Losses	(82)	(75)
Estimated Fair Value	86,508	99,710
Investment securities
Marketable securities and fair value measurements
Amortized Cost	56,719	63,135
Gross Unrealized Gains	12	7
Gross Unrealized Losses	(32)	(39)
Estimated Fair Value	56,699	63,103
Commercial paper
Marketable securities and fair value measurements
Amortized Cost		5,641
Gross Unrealized Gains		1
Gross Unrealized Losses		(2)
Estimated Fair Value		5,640
Investment securities
Marketable securities and fair value measurements
Amortized Cost	29,837	30,985
Gross Unrealized Gains	22	16
Gross Unrealized Losses	(50)	(34)
Estimated Fair Value	$ 29,809	$ 30,967

Marketable Securities and Fai31

Marketable Securities and Fair Value Measurements - Schedule of the Fair Value of the Company's Financial Assets Measured at Fair Value on a Recurring Basis Based on the Three-Tier Value Hierarchy (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Marketable securities and fair value measurements
Total	$ 604,437	$ 305,577
Cash equivalents
Marketable securities and fair value measurements
Money market funds and other funds	512,929	200,867
Commercial paper		5,640
Short-term investments
Marketable securities and fair value measurements
Investment securities	56,699	63,103
Restricted cash
Marketable securities and fair value measurements
Certificate of deposit	5,000	5,000
Long-term marketable securities
Marketable securities and fair value measurements
Investment securities	29,809	30,967
Level 1
Marketable securities and fair value measurements
Total	517,929	205,867
Level 1 | Cash equivalents
Marketable securities and fair value measurements
Money market funds and other funds	512,929	200,867
Commercial paper		0
Level 1 | Short-term investments
Marketable securities and fair value measurements
Investment securities	0	0
Level 1 | Restricted cash
Marketable securities and fair value measurements
Certificate of deposit	5,000	5,000
Level 1 | Long-term marketable securities
Marketable securities and fair value measurements
Investment securities	0	0
Level 2
Marketable securities and fair value measurements
Total	86,508	99,710
Level 2 | Cash equivalents
Marketable securities and fair value measurements
Money market funds and other funds	0	0
Commercial paper		5,640
Level 2 | Short-term investments
Marketable securities and fair value measurements
Investment securities	56,699	63,103
Level 2 | Restricted cash
Marketable securities and fair value measurements
Certificate of deposit	0	0
Level 2 | Long-term marketable securities
Marketable securities and fair value measurements
Investment securities	29,809	30,967
Level 3
Marketable securities and fair value measurements
Total	0	0
Level 3 | Cash equivalents
Marketable securities and fair value measurements
Money market funds and other funds	0	0
Commercial paper		0
Level 3 | Short-term investments
Marketable securities and fair value measurements
Investment securities	0	0
Level 3 | Restricted cash
Marketable securities and fair value measurements
Certificate of deposit	0	0
Level 3 | Long-term marketable securities
Marketable securities and fair value measurements
Investment securities	$ 0	$ 0

Intangible Assets and Goodwil32

Intangible Assets and Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 4,653			$ 4,653	$ 4,653
Accumulated Amortization	(3,191)			(3,191)	(2,347)
Net Book Value	1,462			1,462	2,306
Amortization expense related to intangibles	300	$ 200	$ 600	800
Goodwill	1,900			$ 1,900	$ 1,900
Trademarks
Finite-Lived Intangible Assets [Line Items]
Weighted - Average Amortization Period (Years)				5 years	5 years
Gross Carrying Amount	1,900			$ 1,900	$ 1,900
Accumulated Amortization	(1,583)			(1,583)	(1,298)
Net Book Value	317			$ 317	$ 602
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted - Average Amortization Period (Years)				3 years	3 years
Gross Carrying Amount	1,453			$ 1,453	$ 1,453
Accumulated Amortization	(525)			(525)	(161)
Net Book Value	928			$ 928	$ 1,292
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted - Average Amortization Period (Years)				5 years	5 years
Gross Carrying Amount	1,300			$ 1,300	$ 1,300
Accumulated Amortization	(1,083)			(1,083)	(888)
Net Book Value	$ 217			$ 217	$ 412

Property and Equipment, net (De

Property and Equipment, net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Property and equipment, net
Property and equipment, gross	$ 481,968		$ 481,968		$ 349,685
Less accumulated depreciation and amortization	(163,095)		(163,095)		(110,331)
Property and equipment, net	318,873		318,873		239,354
Depreciation and amortization	22,600	$ 15,200	61,700	$ 37,900
Furniture and computer equipment
Property and equipment, net
Property and equipment, gross	198,903		198,903		133,297
Site and software development costs
Property and equipment, net
Property and equipment, gross	108,456		108,456		77,429
Leasehold improvements
Property and equipment, net
Property and equipment, gross	80,512		80,512		62,090
Construction in progress
Property and equipment, net
Property and equipment, gross	10,416		10,416		47,013
Buildings
Property and equipment, net
Property and equipment, gross	$ 83,681		$ 83,681		$ 29,856

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)wharehouse	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2016USD ($)
Operating Leased Assets [Line Items]
Rental expense under operating leases	$ 10,600	$ 9,100	$ 33,300	$ 23,900
Letter of credit issued as security for lease agreements	13,800		13,800				$ 10,600
Future minimum lease payments for non-cancelable lease							568,700
Additional non-cancelable leases with initial or remaining terms in excess of one year			231,000
Minimum sublease rentals	9,400		9,400
Lease financing obligation	82,725		82,725				$ 28,900
Land lease expense	200		700
Interest expense	2,000		4,900
Future minimum commitments related to financing obligation, principal	6,700		6,700
Future minimum commitments related to financing obligation, interest	$ 39,000		$ 39,000
Warehouse Lease Arrangement | Three Months Ended June 30, 2016
Operating Leased Assets [Line Items]
Letter of credit issued as security for lease agreements								$ 1,200
Warehouse lease arrangements | wharehouse		1
Lease financing obligation								$ 28,900
Warehouse Lease Arrangement | Three Months Ended March 31, 2017
Operating Leased Assets [Line Items]
Letter of credit issued as security for lease agreements						$ 800
Lease financing obligation						$ 12,600
Warehouse Lease Arrangement | Warehouse Lease Arrangement, June 30, 2017
Operating Leased Assets [Line Items]
Letter of credit issued as security for lease agreements					$ 1,000
Lease financing obligation					$ 41,200

Equity-Based Compensation - Nar

Equity-Based Compensation - Narrative (Details) $ in Millions	Oct. 06, 2014vesting_trigger	Sep. 30, 2017USD ($)shares	Jan. 01, 2017shares
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of stock options exercised		$ 4.1
Aggregate intrinsic value of stock options outstanding and repurchased		8.9
Restricted common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of stock unvested		4
Unrecognized share-based compensation		$ 2.7
Weighted average remaining vesting term for options expected to vest		1 year 120 days
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized share-based compensation		$ 231.5
Weighted average remaining vesting term for options expected to vest		1 year 273 days
Intrinsic value of stock vested		$ 99.3
Aggregate intrinsic value		$ 429.6
2014 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized | shares		8,603,066
Number of shares available for future grant | shares			8,389,750
Number of vesting triggers | vesting_trigger	2
Service period	5 years

Equity-Based Compensation - Sum

Equity-Based Compensation - Summary of Activity Relating to Stock Options (Details) - Stock options - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Options
Outstanding at the beginning of the period (in shares)	209,759
Options exercised (in shares)	(72,296)
Outstanding and exercisable at the end of the period (in shares)	137,463	209,759
Weighted- Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 2.98
Options exercised (in dollars per share)	2.92
Outstanding and exercisable at the end of the period (in dollars per share)	$ 3.01	$ 2.98
Weighted- Average Remaining Contractual Term (Years)
Outstanding	3 years 263 days	4 years 6 months

Equity-Based Compensation - S37

Equity-Based Compensation - Summary of Activity Relating to Restricted Stock (Details)	9 Months Ended
	Sep. 30, 2017$ / sharesshares
Restricted stock
Shares
Outstanding at the beginning of the period (in shares) | shares	60,000
Outstanding at the end of the period (in shares) | shares	60,000
Weighted- Average Fair Value
Outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 35.05
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 67.40
RSUs
Shares
Outstanding at the beginning of the period (in shares) | shares	6,986,776
RSUs granted (in shares) | shares	2,271,235
RSUs vested (in shares) | shares	(1,766,511)
RSUs forfeited/canceled (in shares) | shares	(1,117,090)
Outstanding at the end of the period (in shares) | shares	6,374,410
Weighted- Average Fair Value
Outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 34.21
RSUs granted (in dollars per share) | $ / shares	52.39
RSUs vested (in dollars per share) | $ / shares	32.30
RSUs forfeited/canceled (in dollars per share) | $ / shares	37.53
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 41.04

Segment and Geographic Inform38

Segment and Geographic Information - Activity Related to Net Revenue and Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Operations, technology, general and administrative	$ 112,669	$ 79,526	$ 292,988	$ 207,289
Direct Retail	1,181,223	832,398	3,224,036	2,299,901
Other	16,975	29,127	57,843	95,900
Total net revenue	1,198,198	861,525	3,281,879	2,395,801
Adjusted EBITDA	(22,672)	(30,849)	(45,814)	(76,666)
Less: reconciling items	(53,757)	(30,091)	(126,029)	(73,753)
Net loss	(76,429)	(60,940)	(171,843)	(150,419)
Depreciation and amortization	22,913	15,463	62,588	38,528
Equity based compensation and related taxes	19,598	15,308	50,539	37,265
Interest expense (income), net	2,008	292	3,857	(791)
Other expense (income), net	227	(889)	(400)	(1,804)
Provision for (benefit from) income taxes	237	(83)	671	555
Other	8,774	0	8,774	0
Total reconciling items	53,757	30,091	126,029	73,753
Vacated warehouse
Segment Reporting Information [Line Items]
Operations, technology, general and administrative	9,600
U.S.
Segment Reporting Information [Line Items]
Direct Retail	1,033,669	759,674	2,847,898	2,134,782
Other	16,975	28,127	57,843	91,613
Total net revenue	1,050,644	787,801	2,905,741	2,226,395
Adjusted EBITDA	4,531	(7,857)	28,684	(11,816)
International
Segment Reporting Information [Line Items]
Direct Retail	147,554	72,724	376,138	165,119
Other	0	1,000	0	4,287
Total net revenue	147,554	73,724	376,138	169,406
Adjusted EBITDA	(27,203)	$ (22,992)	(74,498)	$ (64,850)
Leasehold improvements
Segment Reporting Information [Line Items]
Depreciation and amortization	800		800
Warehouse Lease Arrangement, July 2017 | Warehouse Lease Arrangement
Segment Reporting Information [Line Items]
Other	$ 8,800		$ 8,800

Segment and Geographic Inform39

Segment and Geographic Information - Schedule of Long-Lived Assets by Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Geographic revenue and long-lived assets
Geographic long-lived assets	$ 318,873	$ 239,354
U.S.
Geographic revenue and long-lived assets
Geographic long-lived assets	311,565	233,099
International
Geographic revenue and long-lived assets
Geographic long-lived assets	$ 7,308	$ 6,255

Income Taxes (Details)

Income Taxes (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 237,000	$ (83,000)	$ 671,000	$ 555,000
Unrecognized tax benefits	$ 0		$ 0		$ 0

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit) (Details)	9 Months Ended	36 Months Ended
	Sep. 30, 2017vote$ / sharesshares	Sep. 30, 2017$ / sharesshares	Dec. 31, 2016$ / sharesshares
Stockholders' Equity
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, par value (in dollars per share) | $ / shares	$ 0.001	$ 0.001
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Class A common stock
Stockholders' Equity
Common stock, shares authorized (in shares)	500,000,000	500,000,000	500,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.001	$ 0.001	$ 0.001
Common stock, shares outstanding (in shares)	56,355,606	56,355,606	49,945,202
Number of votes each holder is entitled | vote	1
Class B common stock
Stockholders' Equity
Common stock, shares authorized (in shares)	164,000,000	164,000,000	164,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.001	$ 0.001	$ 0.001
Common stock, shares outstanding (in shares)	31,290,483	31,290,483	35,885,692
Number of votes each holder is entitled | vote	10
Conversion ratio following the completion of the offering	1
Conversion ratio upon transfer	1
Number of shares converted into Class A shares		43,039,105
Class B common stock | Maximum
Stockholders' Equity
Aggregate number of shares outstanding Class A common stock and Class B common stock that shall convert automatically (less than)	10.00%
Class B common stock | Minimum
Stockholders' Equity
Percentage of outstanding shares of Class B common stock that shall convert automatically in the event of the affirmative vote or written consent of holders	66.67%

Credit Agreement (Details)

Credit Agreement (Details) - USD ($)	Feb. 22, 2017	Dec. 31, 2016	Sep. 11, 2017
Line of credit | Bank of America
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 65,000,000
LIBOR | Line of credit | Bank of America
Line of Credit Facility [Line Items]
Basis spread		1.75%
Credit Card Program
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 40,000,000
Credit Card Program | Line of credit | Bank of America
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 45,000,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	100,000,000
Right to increase	$ 25,000,000
Revolving Credit Facility | Line of credit | Bank of America
Line of Credit Facility [Line Items]
Maximum borrowing capacity		20,000,000
Revolving Credit Facility | Eurodollar
Line of Credit Facility [Line Items]
Basis spread	1.00%
Applicable margin	0.0175
Revolving Credit Facility | Base Rate
Line of Credit Facility [Line Items]
Applicable margin	0.0075
Revolving Credit Facility | Federal Funds Effective Rate
Line of Credit Facility [Line Items]
Basis spread	0.50%
Revolving Credit Facility | Letter of Credit Sublimit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 25,000,000		$ 25,000,000
Revolving Credit Facility | Swing Line Sublimit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 10,000,000
Revolving Credit Facility | Direct Borrowings | Line of credit | Bank of America
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 5,000,000

Convertible Debt (Details)

Convertible Debt (Details)	Sep. 15, 2017USD ($)dayinstitution$ / shares	Sep. 11, 2017$ / shares	Sep. 30, 2017USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)
Debt Instrument [Line Items]
Proceeds from sale of Notes, net of discounts and offering expenses				$ 420,449,000	$ 0
Capped call transaction costs paid from net proceeds				44,160,000	$ 0
Convertible Debt | Three Point Seven Five Percent Senior Note due 2022
Debt Instrument [Line Items]
Debt, face amount	$ 431,250,000
Interest rate, stated percentage	0.375%
Proceeds from sale of Notes, net of discounts and offering expenses	$ 420,400,000
Capped call transaction costs paid from net proceeds	$ 44,200,000
Financial institutions | institution	3
Initial conversion rate	0.00961
Conversion price (in usd per share) | $ / shares	$ 104.06
Number of trading days (whether or not consecutive) | day	20
Minimum trading days immediately preceding date notice of redemption provided | day	1
Trading days immediately preceding date notice of redemption provided | day	5
Number of trading days (consecutive) | day	30
Percentage of conversion stock price	130.00%
During number of business day period	5 days
Consecutive trading day period (after any)	10 days
Principal amount of Notes	$ 1,000
Measurement period, percentage (less than)	98.00%
Redemption price, percentage of principal amount to be redeemed	100.00%
Default percentage of aggregate principal amount of notes outstanding (not less than)	25.00%
Equity component of Notes	$ 95,800,000
Interest expense			$ 900,000	900,000
Accrued interest			900,000	900,000
Debt, fair value			$ 415,000,000	$ 415,000,000
Convertible Debt | Three Point Seven Five Percent Senior Note due 2022 | Class A common stock
Debt Instrument [Line Items]
Cap price, per share (in usd per share) | $ / shares		$ 154.16
Premium over last reported sale price, percentage		100.00%
Convertible Debt | Three Point Seven Five Percent Senior Note due 2022 | Over-Allotment Option
Debt Instrument [Line Items]
Over-allotment option included in issuance of notes	$ 56,250,000

Net Loss per Share - Narrative

Net Loss per Share - Narrative (Details) shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017shares	Sep. 30, 2016shares	Sep. 30, 2017shares	Sep. 30, 2016shares
Class of Stock [Line Items]
Allocation of undistributed earnings between stock classes, conversion ratio			1
Common Stock Options, Restricted Stock Options And Restricted Stock Units
Class of Stock [Line Items]
Antidilutive securities excluded from diluted earnings per share calculation (in shares)	6.6	6.8
Common Stock Options, Restricted Stock Options And Restricted Stock Units | Class A common stock
Class of Stock [Line Items]
Antidilutive securities excluded from diluted earnings per share calculation (in shares)			6.6	6.8

Net Loss per Share - Calculatio

Net Loss per Share - Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net loss	$ (76,429)	$ (60,940)	$ (171,843)	$ (150,419)
Weighted average common shares used for basic and diluted net loss per share computation (in shares)	87,283	85,105	86,679	84,779
Net loss per share:
Basic and Diluted (in dollars per share)	$ (0.88)	$ (0.72)	$ (1.98)	$ (1.77)

Recent Accounting Pronounceme46

Recent Accounting Pronouncements (Details) $ in Millions	Dec. 31, 2016USD ($)
New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2016-09, Forfeiture Rate Component | Retained Earnings
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cumulative-effect adjustment	$ 8.7