Commitments and Letters of Credit - Notional Amount of Commitments and Letter of Credit Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Commitments Net	$ 223	$ 1,087	$ 114
Commitments to extend credit
Loss Contingencies [Line Items]
Financial instrument of credit risk	1,981,275	1,883,914
Financial standby letters of credit
Loss Contingencies [Line Items]
Financial instrument of credit risk	16,630	18,298
Performance standby letters of credit
Loss Contingencies [Line Items]
Financial instrument of credit risk	23,293	22,027
Commercial letters of credit
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 783	$ 887