Revenue from Contracts with Customers (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	$ 118,433	$ 130,804	$ 127,364
Wealth management fees
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	36,806	37,072	36,863
Service charges on deposit accounts
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	35,081	44,915	44,026
Debit card and ATM fees
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	20,178	21,652	20,216
Investment product fees
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	21,614	21,785	20,539
Merchant processing fees
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	3,150	3,105	2,927
Gain (loss) on other real estate owned
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	240	254	1,270
Safe deposit box fees
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	957	1,206	1,124
Insurance premiums and commissions
Disaggregation of Revenue [Line Items]
Noninterest income within scope of Topic 606	$ 407	$ 815	$ 399