Revenue from Contracts with Customers - Revenue from External Customers by Products and Services (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue from External Customer [Line Items]
Total noninterest income in-scope of ASC 606	$ 43,718	$ 43,192
Total noninterest income out-of-scope of ASC 606	11,494	(9,823)
Total noninterest income	55,212	33,369
Insurance commissions
Revenue from External Customer [Line Items]
Total noninterest income in-scope of ASC 606	28,147	27,477
Service charges on deposit accounts
Revenue from External Customer [Line Items]
Total noninterest income in-scope of ASC 606	5,367	6,098
Trust and investment advisory fees
Revenue from External Customer [Line Items]
Total noninterest income in-scope of ASC 606	5,663	5,095
Debit card processing fees
Revenue from External Customer [Line Items]
Total noninterest income in-scope of ASC 606	2,749	2,470
Other non-interest income
Revenue from External Customer [Line Items]
Total noninterest income in-scope of ASC 606	$ 1,792	$ 2,052