Summary of Unrecognized Stock-Based Compensation Expense, Net of Estimated Forfeitures (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Expense, Net of Estimated Forfeitures	$ 59,854
Weighted-average Recognition Period	2 years 7 months 13 days
Restricted stock awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Expense, Net of Estimated Forfeitures	1,571
Weighted-average Recognition Period	3 years 5 months 16 days
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Expense, Net of Estimated Forfeitures	$ 197
Weighted-average Recognition Period	3 months 29 days