Investment Securities - Narrative (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2024 USD ($) position Investment	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) Investment	Dec. 31, 2022 USD ($)
Debt Securities, Available-for-sale [Line Items]
Carrying value of securities pledged to secure public deposits and other contractual obligations	$ 447,800		$ 464,000
Pledging requirements for credit derivatives and SWAP agreements - securities		$ 0	$ 0
Proceeds from Sale of Debt Securities, Available-for-Sale	$ 505	0
Number of investments in non federal issuer representing more than 10% of shareholder's equity | Investment	0		0
Maximum investment in any single non-federal issuer representing shareholders equity	10.00%		10.00%
Fair value HTM in unrealized loss with no ACL	$ 120,463		$ 128,277
Unrealized loss included in fair value of securities HTM in unrealized loss position for which an ACL has not been recorded	14,590		17,500
Fair value AFS in unrealized loss with no ACL	222,279		258,855
Unrealized loss included in fair value of securities AFS in unrealized loss position for which an ACL has not been recorded	29,390		35,629
Fair value of securities AFS in unrealized loss position for which an ACL has been recorded, net of allowance	68,000
Unrealized loss position included in fair value of securities AFS in unrealized loss position for which an ACL has been recorded	6,700
Allowance for credit losses	$ 642		731
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Fair value AFS in unrealized loss with no ACL			780
Unrealized loss included in fair value of securities AFS in unrealized loss position for which an ACL has not been recorded			1
Debt securities, available-for-sale, unrealized loss position, number of positions | position	1
Allowance for credit losses	$ 642	$ 1,537	731	$ 1,140
Number of securities | Investment	33
Available-for-sale Securities
Debt Securities, Available-for-sale [Line Items]
Accrued interest receivable	$ 1,100
Allowance for credit losses	$ 642
Municipal Bonds
Debt Securities, Available-for-sale [Line Items]
Number of securities | Investment	1
U.S. Government Corporations and Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Held-to-maturity, securities in unrealized loss positions, qualitative disclosure, number of positions | position	88
Debt securities, available-for-sale, unrealized loss position, number of positions | position	98
Collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Fair value AFS in unrealized loss with no ACL	$ 1,788		2,001
Unrealized loss included in fair value of securities AFS in unrealized loss position for which an ACL has not been recorded	$ 122		200
Debt securities, available-for-sale, unrealized loss position, number of positions | position	2
Allowance for credit losses	$ 0		$ 0