Investment securities - Amortized Cost and Fair Value of Investment Securities Aggregated by Investment Category (Details) $ in Thousands	Sep. 30, 2020 USD ($) company	Dec. 31, 2019 USD ($)
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	$ 237,209	$ 328,643
Available-for-sale, Gross Unrealized Gains	10,234	2,988
Available-for-sale, Gross Unrealized Losses	39	1,153
Available-for-sale, Fair Value	247,404	330,478
Held-to-maturity, Amortized Cost	7,297	7,656
Held-to-maturity, Gross Unrealized Gains	314	233
Held-to-maturity, Fair value	$ 7,611	7,889
Number of equity securities portfolio consisting of stock of other financial institutions \| company	2
Equity investments carried at fair value	$ 341	423
Fair value of equity portfolio in excess of cost basis	64
U.S. Treasuries
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	21,476	23,966
Available-for-sale, Gross Unrealized Gains	529	162
Available-for-sale, Fair Value	22,005	24,128
U.S. government-sponsored enterprises state and municipals
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	72,876	87,156
Available-for-sale, Gross Unrealized Gains	1,411	181
Available-for-sale, Gross Unrealized Losses		227
Available-for-sale, Fair Value	74,287	87,110
Mortgage-backed Securities, U.S. government agencies
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	4,104	8,368
Available-for-sale, Gross Unrealized Gains	133	112
Available-for-sale, Gross Unrealized Losses	1	10
Available-for-sale, Fair Value	4,236	8,470
Held-to-maturity, Amortized Cost	23	31
Held-to-maturity, Fair value	23	31
Mortgage-backed Securities, U.S. government-sponsored enterprises
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	63,101	101,914
Available-for-sale, Gross Unrealized Gains	2,766	1,011
Available-for-sale, Gross Unrealized Losses	38	77
Available-for-sale, Fair Value	65,829	102,848
Held-to-maturity, Amortized Cost	424	773
Held-to-maturity, Gross Unrealized Gains	16	25
Held-to-maturity, Fair value	440	798
Commercial mortgage-backed Securities, U.S. government-sponsored enterprises
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	12,638	12,694
Available-for-sale, Gross Unrealized Gains	970	171
Available-for-sale, Gross Unrealized Losses		4
Available-for-sale, Fair Value	13,608	12,861
Common equity securities.
Schedule of Trading Securities and Other Trading Assets
Equity investments carried at fair value	341	423
State and Municipals, Taxable
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	31,657	35,418
Available-for-sale, Gross Unrealized Gains	1,871	295
Available-for-sale, Gross Unrealized Losses		815
Available-for-sale, Fair Value	33,528	34,898
State and Municipals, Tax-exempt
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	31,357	59,127
Available-for-sale, Gross Unrealized Gains	2,554	1,056
Available-for-sale, Gross Unrealized Losses		20
Available-for-sale, Fair Value	33,911	60,163
Held-to-maturity, Amortized Cost	6,850	6,852
Held-to-maturity, Gross Unrealized Gains	298	208
Held-to-maturity, Fair value	$ 7,148	$ 7,060

The amount the fair value of the equity portfolio exceeded the cost basis.

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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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Amortized cost 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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