Share-Based Compensation - Unrecognized Compensation Expense (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($)
Unrecognized Share Based Compensation Expense [Line Items]
Unrecognized Expense	$ 67,448
Stock options
Unrecognized Share Based Compensation Expense [Line Items]
Unrecognized Expense	$ 10,935
Average Expected Recognition Period - in Years	2 years 8 months 19 days
Restricted stock units
Unrecognized Share Based Compensation Expense [Line Items]
Unrecognized Expense	$ 56,513
Average Expected Recognition Period - in Years	2 years 8 months 27 days