Property and Equipment, Net - Components of Property and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 122,209	$ 81,221
Less: accumulated depreciation	(48,625)	(37,626)
Construction in progress	7,877
Software and website development projects in progress	67	207
Property and equipment, net	81,528	43,802
Capitalized Software and Website Development [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	73,575	48,527
Property and equipment, net	46,200	28,400
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	21,776	14,244
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	21,124	13,174
Furniture and Other Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 5,734	$ 5,276