Summary of Significant Accounting Policies - Estimated Useful Lives of Property and Equipment (Detail)	12 Months Ended
	Dec. 31, 2013
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Leasehold improvements	Shorter of useful life or remaining duration of lease
Minimum [Member] | Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	2 years
Minimum [Member] | Internal-use Software and Website Development Costs [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Maximum [Member] | Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Maximum [Member] | Internal-use Software and Website Development Costs [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	4 years