SUPPLEMENTAL CONSOLIDATED BALANCE SHEETS AND STATEMENTS OF OPERATIONS INFORMATION - Schedule of Accrued Merchant and Supplier Payables (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Supplemental Consolidated Balance Sheet & Statement of Operations Information [Abstract]
Accrued merchant payables	$ 324,161	$ 459,662
Accrued supplier payables (1)	160,465	310,673
Total accrued merchant and supplier payables	$ 484,626	$ 770,335