Commitments and Letters of Credit - Notional Amount of Commitments and Letter of Credit Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Commitments Net	$ 71	$ 223	$ 1,087
Commitments to extend credit
Loss Contingencies [Line Items]
Financial instrument of credit risk	2,097,628	1,981,275
Financial standby letters of credit
Loss Contingencies [Line Items]
Financial instrument of credit risk	15,988	16,630
Performance standby letters of credit
Loss Contingencies [Line Items]
Financial instrument of credit risk	16,864	23,293
Commercial letters of credit
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 783	$ 783