Securities - Amortized cost and fair value (Details) $ in Thousands	Mar. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Securities available-for-sale:
Available-for-sale, Amortized Cost	$ 50,472	$ 50,942
Available-for-sale, Gross Unrealized Gains	273	119
Available-for-sale, Gross Unrealized Losses	(305)	(633)
Available-for-sale, Fair Value	50,440	50,428
Securities held to maturity:
Held-to-maturity, Amortized Cost	12,712	12,741
Held-to-maturity, Gross Unrealized Gains	113	17
Held-to-maturity, Gross Unrealized (Losses)	(11)	(103)
Fair Value	12,814	12,655
U.S. government agency mortgage-backed securities
Securities available-for-sale:
Available-for-sale, Amortized Cost	23,005	24,092
Available-for-sale, Gross Unrealized Gains	69	45
Available-for-sale, Gross Unrealized Losses	(156)	(271)
Available-for-sale, Fair Value	$ 22,918	$ 23,866
Securities held to maturity:
Number of securities in unrealized loss positions \| security	20	24
U.S. government agency collateralized mortgage obligations
Securities available-for-sale:
Available-for-sale, Amortized Cost	$ 15,419	$ 14,754
Available-for-sale, Gross Unrealized Gains	100	52
Available-for-sale, Gross Unrealized Losses	(114)	(142)
Available-for-sale, Fair Value	$ 15,405	$ 14,664
Securities held to maturity:
Number of securities in unrealized loss positions \| security	10	12
State and municipal securities
Securities available-for-sale:
Available-for-sale, Amortized Cost	$ 11,048	$ 11,096
Available-for-sale, Gross Unrealized Gains	104	22
Available-for-sale, Gross Unrealized Losses	(27)	(199)
Available-for-sale, Fair Value	11,125	10,919
Securities held to maturity:
Held-to-maturity, Amortized Cost	10,718	10,750
Held-to-maturity, Gross Unrealized Gains	113	17
Held-to-maturity, Gross Unrealized (Losses)	(4)	(90)
Fair Value	$ 10,827	$ 10,677
Number of securities in unrealized loss positions \| security	12	26
Investments in mutual funds
Securities available-for-sale:
Available-for-sale, Amortized Cost	$ 1,000	$ 1,000
Available-for-sale, Gross Unrealized Losses	(8)	(21)
Available-for-sale, Fair Value	$ 992	$ 979
Securities held to maturity:
Number of securities in unrealized loss positions \| security	1	1
U.S. Treasuries
Securities held to maturity:
Held-to-maturity, Amortized Cost	$ 1,994	$ 1,991
Held-to-maturity, Gross Unrealized (Losses)	(7)	(13)
Fair Value	$ 1,987	$ 1,978
Number of securities in unrealized loss positions \| security	2	2

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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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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