Revenue from Contracts with Customers - Summary of Topic 606 Revenue Items (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	$ 32,899	$ 31,172	$ 98,205	$ 94,460
Wealth Management Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	9,160	9,022	27,604	27,794
Service Charges on Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	11,860	11,028	34,201	32,552
Debit Card and ATM Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	5,370	4,706	16,292	14,651
Investment Product Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	5,244	5,073	16,106	15,170
Merchant Processing Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	775	779	2,303	2,198
Gain (Loss) on Other Real Estate Owned [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	29	260	194	981
Safe Deposit Box Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	267	221	936	849
Insurance Premiums and Commissions [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	$ 194	$ 83	$ 569	$ 265