Revenue from Contracts with Customers - Summary of Topic 606 Revenue Items (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	$ 127,364	$ 122,416	$ 137,291
Wealth Management Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	36,863	37,316	34,641
Service Charges on Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	44,026	41,331	41,578
Debit Card and ATM Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	20,216	17,676	16,769
Insurance Premiums and Commissions [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	399	617	20,527
Investment Product Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	20,539	20,977	18,822
Merchant Processing Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	2,927	2,634	2,574
Gain (Loss) on Other Real Estate Owned [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	1,270	939	1,419
Safe Deposit Box Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	$ 1,124	$ 926	$ 961