Commitments and Contingencies - Financial Instruments with Off-Balance-Sheet Risk (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Standby Letters of Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	$ 370,718	$ 383,851
Deferred Standby Letter Of Credit Fees [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	1,972	2,236
Commitments to Extend Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	$ 12,053,260	$ 12,137,957