Commitments and Contingent Liabilities - Notional Amount of Outstanding Commitments (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 1,901,550	$ 1,883,914
Financial standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	18,412	18,298
Performance standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	30,026	22,027
Commercial letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 887	$ 887