Investments - Carrying Value and Fair Value of Securities Pledged as Collateral to Secure Public Deposits (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-Sale [Line Items]
Book Value	$ 897,325	$ 803,361
Fair Value	836,868	748,970
Public Fund Deposits [Member]
Debt Securities, Available-for-Sale [Line Items]
Book Value	732,935	509,010
Fair Value	690,855	488,270
Federal Home Loan Bank Pledging [Member]
Debt Securities, Available-for-Sale [Line Items]
Book Value	104,888	84,421
Fair Value	90,406	72,293
Federal Reserve Bank Borrowings [Member]
Debt Securities, Available-for-Sale [Line Items]
Book Value	10,481	158,382
Fair Value	10,358	141,125
Retail Repurchase Agreements [Member]
Debt Securities, Available-for-Sale [Line Items]
Book Value	49,021	51,548
Fair Value	$ 45,249	$ 47,282