Employee Benefit Plans - Schedule of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 26,532	$ 31,826	$ 34,071
Income tax benefit	(8,188)	(10,342)	(9,436)
Stock-based compensation expense, net of tax	18,344	21,484	24,635
RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	21,887	28,952	29,671
ESPP Purchase Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 4,645	2,795	4,003
Employee Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (benefit)		$ 79	$ 397