Share-Based Compensation - Compensation Expense Included in Non-Interest Expense and Related Income Tax Benefits (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Stock Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 344	$ 502	$ 789	$ 987
Income tax benefit	47	81	115	162
Restricted Stock And Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	3,045	3,329	6,322	6,715
Income tax benefit	1,066	1,165	2,213	2,350
Phantom Stock and Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 2,889	$ 2,793	$ 5,942	$ 5,198