Detail of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment	$ 206,952	$ 157,758
Less: accumulated amortization and depreciation	(108,664)	(72,235)
Property and equipment, net	98,288	85,523
Website development costs
Property, Plant and Equipment [Line Items]
Property and equipment	102,130	74,750
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment	28,175	20,965
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	37,923	32,918
Construction-in-progress
Property, Plant and Equipment [Line Items]
Property and equipment	19,470	15,630
Office equipment, furniture, and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment	$ 19,254	$ 13,495