Share-Based Compensation - Unrecognized Compensation Expense (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($)
Unrecognized Share Based Compensation Expense [Line Items]
Unrecognized Expense	$ 75,251
Stock options
Unrecognized Share Based Compensation Expense [Line Items]
Unrecognized Expense	$ 12,309
Average Expected Recognition Period - in Years	2 years 10 months 17 days
Restricted stock units
Unrecognized Share Based Compensation Expense [Line Items]
Unrecognized Expense	$ 62,942
Average Expected Recognition Period - in Years	2 years 10 months 21 days