Commitments and Contingent Liabilities - Notional Amount of Outstanding Commitments (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 1,990,464	$ 1,883,914
Financial standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	18,289	18,298
Performance standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	25,249	22,027
Commercial letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 783	$ 887