Investment securities - Amortized Cost and Fair Value of Investment Securities Aggregated by Investment Category (Details) $ in Thousands	Jun. 30, 2019 USD ($) company	Dec. 31, 2018 USD ($)
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	$ 259,888	$ 272,933
Available-for-sale, Gross Unrealized Gains	2,361	757
Available-for-sale, Gross Unrealized Losses	584	4,008
Available-for-sale, Fair Value	261,665	269,682
Held-to-maturity, Amortized Cost	7,969	8,361
Held-to-maturity, Gross Unrealized Gains	183	67
Held-to-maturity, Gross Unrealized Losses	1	48
Held-to-maturity, Fair value	8,151	8,380
Equity investments carried at fair value	$ 283	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	$ 6
Mortgage-backed Securities, U.S. Government agencies
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	10,669	12,663
Available-for-sale, Gross Unrealized Gains	135	50
Available-for-sale, Gross Unrealized Losses	20	84
Available-for-sale, Fair Value	10,784	12,629
Held-to-maturity, Amortized Cost	36	42
Held-to-maturity, Fair value	36	42
Mortgage-backed Securities, U.S. Government-sponsored enterprises
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	40,901	33,149
Available-for-sale, Gross Unrealized Gains	776	49
Available-for-sale, Gross Unrealized Losses	92	401
Available-for-sale, Fair Value	41,585	32,797
Held-to-maturity, Amortized Cost	1,079	1,464
Held-to-maturity, Gross Unrealized Gains	32	55
Held-to-maturity, Gross Unrealized Losses	1	5
Held-to-maturity, Fair value	1,110	1,514
Commercial mortgage-backed Securities, U.S. Government-sponsored enterprises
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	8,601	6,269
Available-for-sale, Gross Unrealized Gains	145
Available-for-sale, Gross Unrealized Losses		230
Available-for-sale, Fair Value	8,746	6,039
U.S. Government-sponsored enterprises state and municipals
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	93,830	94,999
Available-for-sale, Gross Unrealized Gains	82	2
Available-for-sale, Gross Unrealized Losses	423	2,183
Available-for-sale, Fair Value	93,489	92,818
U.S. Treasuries
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	23,958	25,948
Available-for-sale, Gross Unrealized Gains	143	9
Available-for-sale, Gross Unrealized Losses	17	365
Available-for-sale, Fair Value	24,084	25,592
Common equity securities.
Schedule of Trading Securities and Other Trading Assets
Equity investments carried at fair value	283	291
State and Municipals, Taxable
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	12,475	13,544
Available-for-sale, Gross Unrealized Gains	367	309
Available-for-sale, Fair Value	12,842	13,853
State and Municipals, Tax-exempt
Schedule of Trading Securities and Other Trading Assets
Available-for-sale, Amortized Cost	69,454	86,361
Available-for-sale, Gross Unrealized Gains	713	338
Available-for-sale, Gross Unrealized Losses	32	745
Available-for-sale, Fair Value	70,135	85,954
Held-to-maturity, Amortized Cost	6,854	6,855
Held-to-maturity, Gross Unrealized Gains	151	12
Held-to-maturity, Gross Unrealized Losses		43
Held-to-maturity, Fair value	$ 7,005	$ 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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