Commitments and Contingencies	6 Months Ended
Jun. 30, 2018
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 2031 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 $15.3 million and $11.1 million in the three months ended June 30, 2018 and 2017, respectively, and $28.9 million and $22.6 million in the six months ended June 30, 2018 and 2017, respectively. The Company has issued letters of credit for approximately $26.1 million and $15.3 million as security for these lease agreements as of June 30, 2018 and December 31, 2017, respectively. As of December 31, 2017, the future minimum rental commitments under non-cancelable leases with initial or remaining terms in excess of one year totaled $783.7 million. Subsequent to December 31, 2017, 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 $218.8 million. Future lease payments have not been reduced by minimum sublease rentals of $5.5 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 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 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 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. The construction of a fourth warehouse lease arrangement was completed in the three months ended June 30, 2018, and because the Company had a letter of credit of $2.5 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, $41.2 million and $58.0 million was recorded in "Lease financing obligation, net of current portion" and "Property and equipment, net" in the Company’s unaudited consolidated and condensed balance sheets as of June 30, 2016, March 31, 2017, June 30, 2017, and June 30, 2018 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 six months ended June 30, 2018, land lease expense was $0.7 million and $1.3 million, respectively, and interest expense on lease financing obligations was $2.5 million and $4.5 million, respectively. As of June 30, 2018, future minimum commitments related to the financing obligations were $12.9 million and $66.3 million for principal and interest, respectively, through June 30, 2023. Collection of Sales or Other Similar Taxes The Company has historically collected and remitted sales tax based on the locations of its physical operations. On June 21, 2018, the U.S. Supreme Court rendered a 5-4 majority decision in South Dakota v. Wayfair Inc., 17-494. Among other things, the Court held that a state may require an out-of-state seller with no physical presence in the state to collect and remit sales taxes on goods the seller ships to consumers in the state, overturning existing court precedent. Several states and other taxing jurisdictions have presented, or indicated that they may present, the Company with sales tax assessments. The aggregate assessments received as of June 30, 2018 are not material to the Company's business and the Company does not expect the Court's decision to have a significant impact on its business. Legal Matters On June 21, 2018, the U.S. Supreme Court rendered a 5-4 majority decision in South Dakota v. Wayfair Inc., 17-494. Among other things, the Court held that a state may require an out-of-state seller with no physical presence in the state to collect and remit sales taxes on goods the seller ships to consumers in the state, overturning existing court precedent. See Collection of Sales or Other Similar Taxes above. 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.

Commitments and Contingencies

Leases

The Company leases office and warehouse spaces under non-cancelable leases. These leases expire at various dates through 2031 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 $15.3 million and $11.1 million in the three months ended June 30, 2018 and 2017, respectively, and $28.9 million and $22.6 million in the six months ended June 30, 2018 and 2017, respectively. The Company has issued letters of credit for approximately $26.1 million and $15.3 million as security for these lease agreements as of June 30, 2018 and December 31, 2017, respectively.

As of December 31, 2017, the future minimum rental commitments under non-cancelable leases with initial or remaining terms in excess of one year totaled $783.7 million. Subsequent to December 31, 2017, 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 $218.8 million. Future lease payments have not been reduced by minimum sublease rentals of $5.5 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 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 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 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. The construction of a fourth warehouse lease arrangement was completed in the three months ended June 30, 2018, and because the Company had a letter of credit of $2.5 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, $41.2 million and $58.0 million was recorded in "Lease financing obligation, net of current portion" and "Property and equipment, net" in the Company’s unaudited consolidated and condensed balance sheets as of June 30, 2016, March 31, 2017, June 30, 2017, and June 30, 2018 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 six months ended June 30, 2018, land lease expense was $0.7 million and $1.3 million, respectively, and interest expense on lease financing obligations was $2.5 million and $4.5 million, respectively. As of June 30, 2018, future minimum commitments related to the financing obligations were $12.9 million and $66.3 million for principal and interest, respectively, through June 30, 2023.

Collection of Sales or Other Similar Taxes

The Company has historically collected and remitted sales tax based on the locations of its physical operations. On June 21, 2018, the U.S. Supreme Court rendered a 5-4 majority decision in South Dakota v. Wayfair Inc., 17-494. Among other things, the Court held that a state may require an out-of-state seller with no physical presence in the state to collect and remit sales taxes on goods the seller ships to consumers in the state, overturning existing court precedent. Several states and other taxing jurisdictions have presented, or indicated that they may present, the Company with sales tax assessments. The aggregate assessments received as of June 30, 2018 are not material to the Company's business and the Company does not expect the Court's decision to have a significant impact on its business.

Legal Matters

On June 21, 2018, the U.S. Supreme Court rendered a 5-4 majority decision in South Dakota v. Wayfair Inc., 17-494. Among other things, the Court held that a state may require an out-of-state seller with no physical presence in the state to collect and remit sales taxes on goods the seller ships to consumers in the state, overturning existing court precedent. See Collection of Sales or Other Similar Taxes above.

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.