Commitments and Contingent Liabilities - Notional Amount of Outstanding Commitments (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 2,080,476	$ 1,981,275
Financial standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	13,879	16,630
Performance standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	17,914	23,293
Commercial letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 470	$ 783