Investment securities - Amortized Cost and Fair Value of Investment Securities Aggregated by Investment Category (Details) $ in Thousands	Sep. 30, 2019 USD ($) company	Dec. 31, 2018 USD ($)
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	$ 266,886	$ 272,933
Available-for-sale, Gross Unrealized Gains	2,644	757
Available-for-sale, Gross Unrealized Losses	707	4,008
Available-for-sale, Fair Value	268,823	269,682
Held-to-maturity, Amortized Cost	7,808	8,361
Held-to-maturity, Gross Unrealized Gains	209	67
Held-to-maturity, Gross Unrealized Losses	1	48
Held-to-maturity, Fair value	8,016	8,380
Equity investments carried at fair value	$ 297	291
Number of equity securities portfolio consisting of stock of other financial institutions \| company	2
Fair value of equity portfolio in excess of cost basis	$ 20
Mortgage-backed Securities, U.S. Government agencies
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	9,536	12,663
Available-for-sale, Gross Unrealized Gains	95	50
Available-for-sale, Gross Unrealized Losses	18	84
Available-for-sale, Fair Value	9,613	12,629
Held-to-maturity, Amortized Cost	33	42
Held-to-maturity, Fair value	33	42
Mortgage-backed Securities, U.S. Government-sponsored enterprises
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	45,284	33,149
Available-for-sale, Gross Unrealized Gains	820	49
Available-for-sale, Gross Unrealized Losses	63	401
Available-for-sale, Fair Value	46,041	32,797
Held-to-maturity, Amortized Cost	922	1,464
Held-to-maturity, Gross Unrealized Gains	27	55
Held-to-maturity, Gross Unrealized Losses	1	5
Held-to-maturity, Fair value	948	1,514
Commercial mortgage-backed Securities, U.S. Government-sponsored enterprises
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	13,694	6,269
Available-for-sale, Gross Unrealized Gains	236
Available-for-sale, Gross Unrealized Losses		230
Available-for-sale, Fair Value	13,930	6,039
U.S. Government-sponsored enterprises state and municipals
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	92,223	94,999
Available-for-sale, Gross Unrealized Gains	107	2
Available-for-sale, Gross Unrealized Losses	340	2,183
Available-for-sale, Fair Value	91,990	92,818
U.S. Treasuries
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	23,963	25,948
Available-for-sale, Gross Unrealized Gains	120	9
Available-for-sale, Gross Unrealized Losses	17	365
Available-for-sale, Fair Value	24,066	25,592
Common equity securities.
Schedule of Trading Securities and Other Trading Assets
Equity investments carried at fair value	297	291
State and Municipals, Taxable
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	21,392	13,544
Available-for-sale, Gross Unrealized Gains	346	309
Available-for-sale, Gross Unrealized Losses	238
Available-for-sale, Fair Value	21,500	13,853
State and Municipals, Tax-exempt
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	60,794	86,361
Available-for-sale, Gross Unrealized Gains	920	338
Available-for-sale, Gross Unrealized Losses	31	745
Available-for-sale, Fair Value	61,683	85,954
Held-to-maturity, Amortized Cost	6,853	6,855
Held-to-maturity, Gross Unrealized Gains	182	12
Held-to-maturity, Gross Unrealized Losses		43
Held-to-maturity, Fair value	$ 7,035	$ 6,824

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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