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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 336	$ 319	$ 685	$ 631
Income tax benefit	24	23	50	46
Restricted Stock And Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	5,931	4,927	11,154	9,349
Income tax benefit	1,245	1,035	2,342	1,963
Phantom Stock and Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 2,451	$ 2,017	$ 5,645	$ 5,013