Summary of Significant Accounting Policies - Estimated Useful Lives of Assets (Detail)	3 Months Ended
	Mar. 31, 2013
Computer equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	3 years
Software [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	3 years
Furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	5 years
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of Leasehold improvements	Shorter of life of lease or estimated useful life