Investment securities - Amortized Cost and Fair Value of Investment Securities Aggregated by Investment Category (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Investment Securities
Available-for-sale, Amortized Cost	$ 473,620	$ 543,953
Available-for-sale, Gross Unrealized Gains	6	93
Available-for-sale, Gross Unrealized Losses	55,501	66,343
Available-for-sale, Fair Value	418,125	477,703
Held-to-maturity, Amortized Cost	89,705	91,179
Held-to-maturity, Gross Unrealized Gains	8	1
Held-to-maturity, Gross Unrealized Losses	12,640	14,617
Held-to-maturity, Fair value	77,073	76,563
U.S. Treasury securities
Investment Securities
Available-for-sale, Amortized Cost	197,660	199,937
Available-for-sale, Gross Unrealized Losses	16,096	19,640
Available-for-sale, Fair Value	181,564	180,297
U.S. Government-sponsored enterprises state and municipals
Investment Securities
Available-for-sale, Amortized Cost	16,872	16,955
Available-for-sale, Gross Unrealized Losses	441	585
Available-for-sale, Fair Value	16,431	16,370
State and municipals, Taxable
Investment Securities
Available-for-sale, Amortized Cost	68,426	68,946
Available-for-sale, Gross Unrealized Gains	5
Available-for-sale, Gross Unrealized Losses	11,227	13,588
Available-for-sale, Fair Value	57,204	55,358
State and municipals, Tax-exempt
Investment Securities
Available-for-sale, Amortized Cost	77,668	99,774
Available-for-sale, Gross Unrealized Gains	1	93
Available-for-sale, Gross Unrealized Losses	9,095	11,460
Available-for-sale, Fair Value	68,574	88,407
Tax-exempt state and municipals
Investment Securities
Held-to-maturity, Amortized Cost	11,228	11,237
Held-to-maturity, Gross Unrealized Gains	8	1
Held-to-maturity, Gross Unrealized Losses	674	841
Held-to-maturity, Fair value	10,562	10,397
Residential mortgage-backed securities, U.S. government agencies
Investment Securities
Available-for-sale, Amortized Cost	942	982
Available-for-sale, Gross Unrealized Losses	34	40
Available-for-sale, Fair Value	908	942
Held-to-maturity, Amortized Cost	16,806	17,304
Held-to-maturity, Gross Unrealized Losses	2,541	3,016
Held-to-maturity, Fair value	14,265	14,288
Residential mortgage-backed securities, U.S. government-sponsored enterprises
Investment Securities
Available-for-sale, Amortized Cost	95,947	141,231
Available-for-sale, Gross Unrealized Losses	17,735	20,112
Available-for-sale, Fair Value	78,212	121,119
Held-to-maturity, Amortized Cost	61,671	62,638
Held-to-maturity, Gross Unrealized Losses	9,425	10,760
Held-to-maturity, Fair value	52,246	51,878
Commercial mortgage-backed Securities, U.S. government-sponsored enterprises
Investment Securities
Available-for-sale, Amortized Cost	12,105	12,128
Available-for-sale, Gross Unrealized Losses	484	544
Available-for-sale, Fair Value	11,621	11,584
Corporate debt securities
Investment Securities
Available-for-sale, Amortized Cost	4,000	4,000
Available-for-sale, Gross Unrealized Losses	389	374
Available-for-sale, Fair Value	$ 3,611	$ 3,626

Amount, before tax, of unrealized gain 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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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 excluding accrued interest, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

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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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