Revenue from Contracts with Customers - Summary of Topic 606 Revenue Items (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	$ 31,493	$ 30,965
Wealth Management Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	8,535	9,026
Service Charges on Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	10,826	10,759
Debit Card and ATM Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	5,503	4,865
Investment Product Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	5,271	5,031
Merchant Processing Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	707	641
Gain (Loss) on Other Real Estate Owned [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	40	135
Safe Deposit Box Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	411	404
Insurance Premiums and Commissions [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income within scope of Topic 606	$ 200	$ 104