Investments - Carrying Value of Securities Pledged as Collateral to Secure Public Deposits (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Carrying value of securities pledged as collateral	$ 969,940	$ 909,275
Public Fund Deposits [Member]
Debt Securities, Available-for-Sale [Line Items]
Carrying value of securities pledged as collateral	777,425	820,751
Federal Reserve Bank Borrowings [Member]
Debt Securities, Available-for-Sale [Line Items]
Carrying value of securities pledged as collateral	147,642	33,235
Retail Repurchase Agreements [Member]
Debt Securities, Available-for-Sale [Line Items]
Carrying value of securities pledged as collateral	$ 44,873	$ 55,289