Investment securities - Amortized Cost and Fair Value of Investment Securities Aggregated by Investment Category (Details) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) security
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	$ 272,933	$ 328,643
Available-for-sale, Gross Unrealized Gains	757	2,988
Available-for-sale, Gross Unrealized Losses	4,008	1,153
Available-for-sale, Fair Value	269,682	330,478
Held-to-maturity, Amortized Cost	8,361	7,656
Held-to-maturity, Gross Unrealized Gains	67	233
Held-to-maturity, Gross Unrealized Losses	48
Held-to-maturity, Fair value	8,380	7,889
Equity investments carried at fair value	291	$ 423
Number of equity securities portfolio consisting of stock of other financial institutions \| security		2
Net unrealized gains recognized in AOCI	3
Mortgage-backed Securities, U.S. government agencies
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	12,663	$ 8,368
Available-for-sale, Gross Unrealized Gains	50	112
Available-for-sale, Gross Unrealized Losses	84	10
Available-for-sale, Fair Value	12,629	8,470
Held-to-maturity, Amortized Cost	42	31
Held-to-maturity, Fair value	42	31
Mortgage-backed Securities, U.S. government-sponsored enterprises
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	33,149	101,914
Available-for-sale, Gross Unrealized Gains	49	1,011
Available-for-sale, Gross Unrealized Losses	401	77
Available-for-sale, Fair Value	32,797	102,848
Held-to-maturity, Amortized Cost	1,464	773
Held-to-maturity, Gross Unrealized Gains	55	25
Held-to-maturity, Gross Unrealized Losses	5
Held-to-maturity, Fair value	1,514	798
Commercial mortgage-backed Securities, U.S. government-sponsored enterprises
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	6,269	12,694
Available-for-sale, Gross Unrealized Gains		171
Available-for-sale, Gross Unrealized Losses	230	4
Available-for-sale, Fair Value	6,039	12,861
U.S. government-sponsored enterprises state and municipals
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	94,999	87,156
Available-for-sale, Gross Unrealized Gains	2	181
Available-for-sale, Gross Unrealized Losses	2,183	227
Available-for-sale, Fair Value	92,818	87,110
U.S. Treasuries
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	25,948	23,966
Available-for-sale, Gross Unrealized Gains	9	162
Available-for-sale, Gross Unrealized Losses	365
Available-for-sale, Fair Value	25,592	24,128
Common equity securities.
Schedule of Trading Securities and Other Trading Assets
Equity investments carried at fair value	291	423
State and Municipals, Taxable
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	13,544	35,418
Available-for-sale, Gross Unrealized Gains	309	295
Available-for-sale, Gross Unrealized Losses		815
Available-for-sale, Fair Value	13,853	34,898
Held-to-maturity, Amortized Cost		6,852
Held-to-maturity, Gross Unrealized Gains		208
Held-to-maturity, Fair value		7,060
State and Municipals, Tax-exempt
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	86,361	59,127
Available-for-sale, Gross Unrealized Gains	338	1,056
Available-for-sale, Gross Unrealized Losses	745	20
Available-for-sale, Fair Value	85,954	$ 60,163
Held-to-maturity, Amortized Cost	6,855
Held-to-maturity, Gross Unrealized Gains	12
Held-to-maturity, Gross Unrealized Losses	43
Held-to-maturity, Fair value	$ 6,824

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

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The amount of other than temporary impairment losses on investments in equity securities which have been recognized in earnings during the period.

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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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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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