Class A Common Stock Reserved for Future Issuance (Detail) (Class A Common Stock) In Thousands, unless otherwise specified	Dec. 31, 2014
Class Of Stock [Line Items]
Total shares restricted for future use	35,361
Stock Incentive Plan
Class Of Stock [Line Items]
Total shares restricted for future use	3,118
Outstanding Stock Option
Class Of Stock [Line Items]
Total shares restricted for future use	15,601
Note Warrant hedge
Class Of Stock [Line Items]
Total shares restricted for future use	10,001
For Series B to A conversion
Class Of Stock [Line Items]
Total shares restricted for future use	4,801
Employee stock purchase plan
Class Of Stock [Line Items]
Total shares restricted for future use	1,840