Investment securities - Amortized Cost and Fair Value of Investment Securities Aggregated by Investment Category (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Investment Securities
Available-for-sale, Amortized Cost	$ 448,381	$ 450,454
Available-for-sale, Gross Unrealized Losses	53,968	51,527
Available-for-sale	394,413	398,927
Held-to-maturity, Amortized Cost	83,306	84,851
Held-to-maturity, Gross Unrealized Gains	1	1
Held-to-maturity, Gross Unrealized Losses	13,318	13,154
Held-to-maturity, Fair value	69,989	71,698
U.S. Treasury securities
Investment Securities
Available-for-sale, Amortized Cost	198,006	197,920
Available-for-sale, Gross Unrealized Losses	14,107	13,863
Available-for-sale	183,899	184,057
U.S. Government-sponsored enterprises state and municipals
Investment Securities
Available-for-sale, Amortized Cost	2,412	2,539
Available-for-sale, Gross Unrealized Losses	376	387
Available-for-sale	2,036	2,152
State and municipals, Taxable
Investment Securities
Available-for-sale, Amortized Cost	67,796	67,831
Available-for-sale, Gross Unrealized Losses	10,883	10,731
Available-for-sale	56,913	57,100
State and municipals, Tax-exempt
Investment Securities
Available-for-sale, Amortized Cost	75,542	75,742
Available-for-sale, Gross Unrealized Losses	8,983	8,618
Available-for-sale	66,559	67,124
Tax-exempt state and municipals
Investment Securities
Held-to-maturity, Amortized Cost	11,192	11,201
Held-to-maturity, Gross Unrealized Gains	1	1
Held-to-maturity, Gross Unrealized Losses	709	660
Held-to-maturity, Fair value	10,484	10,542
Residential mortgage-backed securities, U.S. government agencies
Investment Securities
Available-for-sale, Amortized Cost	702	758
Available-for-sale, Gross Unrealized Losses	37	34
Available-for-sale	665	724
Held-to-maturity, Amortized Cost	14,928	15,400
Held-to-maturity, Gross Unrealized Losses	2,644	2,653
Held-to-maturity, Fair value	12,284	12,747
Residential mortgage-backed securities, U.S. government-sponsored enterprises
Investment Securities
Available-for-sale, Amortized Cost	88,488	89,935
Available-for-sale, Gross Unrealized Losses	18,989	17,264
Available-for-sale	69,499	72,671
Held-to-maturity, Amortized Cost	57,186	58,250
Held-to-maturity, Gross Unrealized Losses	9,965	9,841
Held-to-maturity, Fair value	47,221	48,409
Commercial mortgage-backed Securities, U.S. government-sponsored enterprises
Investment Securities
Available-for-sale, Amortized Cost	11,435	11,729
Available-for-sale, Gross Unrealized Losses	336	360
Available-for-sale	11,099	11,369
Corporate Debt Securities
Investment Securities
Available-for-sale, Amortized Cost	4,000	4,000
Available-for-sale, Gross Unrealized Losses	257	270
Available-for-sale	$ 3,743	$ 3,730

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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