Share-Based Compensation (Costs Associated with Share-Based Compensation Plans) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	$ 7,758	$ 7,626	$ 27,355	$ 27,135
RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	6,805	6,652	25,153	25,178
Employee stock purchase plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	$ 953	$ 974	$ 2,202	$ 1,957