Share-Based Compensation (Expenses Associated with Share-Based Compensation Plans) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	$ 6,617	$ 6,128	$ 31,196	$ 28,096
RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	5,866	5,401	28,634	25,766
Stock options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	69	68	203	203
Employee stock purchase plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	$ 682	$ 659	$ 2,359	$ 2,127