Revenue from Contracts with Customers (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	$ 27,828	$ 33,813	$ 58,835	$ 65,306
Wealth management fees
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	9,424	9,909	18,308	18,444
Service charges on deposit accounts
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	7,582	11,515	17,659	22,341
Debit card and ATM fees
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	4,832	5,419	9,830	10,922
Investment product fees
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	4,845	5,591	10,719	10,862
Merchant processing fees
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	707	821	1,511	1,528
Gain (loss) on other real estate owned
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	34	125	(22)	165
Safe deposit box fees
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	208	258	518	669
Insurance premiums and commissions
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	$ 196	$ 175	$ 312	$ 375