Commitments and Contingent Liabilities - Notional Amount of Outstanding Commitments (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 2,136,708	$ 2,097,628
Financial standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	16,331	15,988
Performance standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	17,393	16,864
Commercial letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 766	$ 783