Investment securities - Amortized Cost and Fair Value of Investment Securities Aggregated by Investment Category (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Investment Securities
Available-for-sale, Amortized Cost	$ 286,215	$ 328,643
Available-for-sale, Gross Unrealized Gains	9,899	2,988
Available-for-sale, Gross Unrealized Losses	203	1,153
Available-for-sale, Fair Value	295,911	330,478
Held-to-maturity, Amortized Cost	7,225	7,656
Held-to-maturity, Gross Unrealized Gains	288	233
Held-to-maturity, Fair value	7,513	7,889
U.S. Treasuries
Investment Securities
Available-for-sale, Amortized Cost	18,478	23,966
Available-for-sale, Gross Unrealized Gains	427	162
Available-for-sale, Fair Value	18,905	24,128
U.S. government-sponsored enterprises state and municipals
Investment Securities
Available-for-sale, Amortized Cost	63,834	87,156
Available-for-sale, Gross Unrealized Gains	1,354	181
Available-for-sale, Gross Unrealized Losses		227
Available-for-sale, Fair Value	65,188	87,110
Mortgage-backed Securities, U.S. government agencies
Investment Securities
Available-for-sale, Amortized Cost	3,553	8,368
Available-for-sale, Gross Unrealized Gains	154	112
Available-for-sale, Gross Unrealized Losses		10
Available-for-sale, Fair Value	3,707	8,470
Held-to-maturity, Amortized Cost	21	31
Held-to-maturity, Fair value	21	31
Mortgage-backed Securities, U.S. government-sponsored enterprises
Investment Securities
Available-for-sale, Amortized Cost	79,457	101,914
Available-for-sale, Gross Unrealized Gains	1,930	1,011
Available-for-sale, Gross Unrealized Losses	136	77
Available-for-sale, Fair Value	81,251	102,848
Held-to-maturity, Amortized Cost	355	773
Held-to-maturity, Gross Unrealized Gains	13	25
Held-to-maturity, Fair value	368	798
Commercial mortgage-backed Securities, U.S. government-sponsored enterprises
Investment Securities
Available-for-sale, Amortized Cost	12,619	12,694
Available-for-sale, Gross Unrealized Gains	881	171
Available-for-sale, Gross Unrealized Losses		4
Available-for-sale, Fair Value	13,500	12,861
Corporate debt securities
Investment Securities
Available-for-sale, Amortized Cost	1,000
Available-for-sale, Fair Value	1,000
State and Municipals, Taxable
Investment Securities
Available-for-sale, Amortized Cost	53,297	35,418
Available-for-sale, Gross Unrealized Gains	2,099	295
Available-for-sale, Gross Unrealized Losses	30	815
Available-for-sale, Fair Value	55,366	34,898
Held-to-maturity, Amortized Cost	6,849
Held-to-maturity, Gross Unrealized Gains	275
Held-to-maturity, Fair value	7,124
State and Municipals, Tax-exempt
Investment Securities
Available-for-sale, Amortized Cost	53,977	59,127
Available-for-sale, Gross Unrealized Gains	3,054	1,056
Available-for-sale, Gross Unrealized Losses	37	20
Available-for-sale, Fair Value	$ 56,994	60,163
Held-to-maturity, Amortized Cost		6,852
Held-to-maturity, Gross Unrealized Gains		208
Held-to-maturity, Fair value		$ 7,060

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

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