Investment securities - Amortized Cost and Fair Value of Investment Securities Aggregated by Investment Category (Details) $ in Thousands	Jun. 30, 2020 USD ($) company	Dec. 31, 2019 USD ($)
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	$ 276,418	$ 328,643
Available-for-sale, Gross Unrealized Gains	11,302	2,988
Available-for-sale, Gross Unrealized Losses	11	1,153
Available-for-sale, Fair Value	287,709	330,478
Held-to-maturity, Amortized Cost	7,401	7,656
Held-to-maturity, Gross Unrealized Gains	316	233
Held-to-maturity, Fair value	7,717	7,889
Equity investments carried at fair value	$ 338	423
Number of equity securities portfolio consisting of stock of other financial institutions \| company	2
Fair value of equity portfolio in excess of cost basis	$ 61
Mortgage-backed Securities, U.S. government agencies
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	5,717	8,368
Available-for-sale, Gross Unrealized Gains	154	112
Available-for-sale, Gross Unrealized Losses	4	10
Available-for-sale, Fair Value	5,867	8,470
Held-to-maturity, Amortized Cost	26	31
Held-to-maturity, Fair value	26	31
Mortgage-backed Securities, U.S. government-sponsored enterprises
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	89,787	101,914
Available-for-sale, Gross Unrealized Gains	4,057	1,011
Available-for-sale, Gross Unrealized Losses	7	77
Available-for-sale, Fair Value	93,837	102,848
Held-to-maturity, Amortized Cost	525	773
Held-to-maturity, Gross Unrealized Gains	22	25
Held-to-maturity, Fair value	547	798
Commercial mortgage-backed Securities, U.S. government-sponsored enterprises
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	12,657	12,694
Available-for-sale, Gross Unrealized Gains	984	171
Available-for-sale, Gross Unrealized Losses		4
Available-for-sale, Fair Value	13,641	12,861
U.S. government-sponsored enterprises state and municipals
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	79,473	87,156
Available-for-sale, Gross Unrealized Gains	1,628	181
Available-for-sale, Gross Unrealized Losses		227
Available-for-sale, Fair Value	81,101	87,110
U.S. Treasuries
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	21,473	23,966
Available-for-sale, Gross Unrealized Gains	604	162
Available-for-sale, Fair Value	22,077	24,128
Common equity securities.
Schedule of Trading Securities and Other Trading Assets
Equity investments carried at fair value	338	423
State and Municipals, Taxable
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	31,694	35,418
Available-for-sale, Gross Unrealized Gains	1,467	295
Available-for-sale, Gross Unrealized Losses		815
Available-for-sale, Fair Value	33,161	34,898
State and Municipals, Tax-exempt
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	35,617	59,127
Available-for-sale, Gross Unrealized Gains	2,408	1,056
Available-for-sale, Gross Unrealized Losses		20
Available-for-sale, Fair Value	38,025	60,163
Held-to-maturity, Amortized Cost	6,850	6,852
Held-to-maturity, Gross Unrealized Gains	294	208
Held-to-maturity, Fair value	$ 7,144	$ 7,060

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

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The number of equity securities portfolio consisting of stock of other financial institutions.

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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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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 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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