SUPPLEMENTAL CONSOLIDATED BALANCE SHEETS AND STATEMENTS OF OPERATIONS INFORMATION - Schedule of Accrued Merchant and Supplier Payables (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Supplemental Consolidated Balance Sheet & Statement of Operations Information [Abstract]
Accrued merchant payables		$ 377,097	$ 459,662
Accrued supplier payables (1)	[1]	151,127	310,673
Total accrued merchant and supplier payables		$ 528,224	$ 770,335

[1] (1)Amounts include payables to suppliers of inventories and providers of shipping and fulfillment services.