Securities - Amortized cost and fair value (Details) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Securities available-for-sale:
Amortized Cost	$ 101,471	$ 58,874
Available-for-sale, Gross Unrealized Gains	2,319	366
Available-for-sale, Gross Unrealized Losses	(432)	(384)
Securities available-for-sale	103,358	58,856
Securities held to maturity:
Held-to-maturity, Amortized Cost	6,544	8,780
Held-to-maturity, Gross Unrealized Gains	372	223
Fair Value	$ 6,916	$ 9,003
Number of securities deemed other-than-temporarily impaired \| security	0	0
U.S. asset backed securities
Securities available-for-sale:
Amortized Cost	$ 24,705	$ 11,967
Available-for-sale, Gross Unrealized Gains	211
Available-for-sale, Gross Unrealized Losses	(172)	(101)
Securities available-for-sale	$ 24,744	$ 11,866
Securities held to maturity:
Number of securities in unrealized loss positions \| security	14	9
U.S. government agency mortgage-backed securities
Securities available-for-sale:
Amortized Cost	$ 3,919	$ 5,457
Available-for-sale, Gross Unrealized Gains	192	66
Available-for-sale, Gross Unrealized Losses		(26)
Securities available-for-sale	4,111	$ 5,497
Securities held to maturity:
Number of securities in unrealized loss positions \| security		1
U.S. government agency collateralized mortgage obligations
Securities available-for-sale:
Amortized Cost	21,375	$ 35,096
Available-for-sale, Gross Unrealized Gains	1,108	300
Available-for-sale, Gross Unrealized Losses		(173)
Securities available-for-sale	$ 22,483	$ 35,223
Securities held to maturity:
Number of securities in unrealized loss positions \| security	1	15
State and municipal securities
Securities available-for-sale:
Amortized Cost	$ 48,789	$ 6,354
Available-for-sale, Gross Unrealized Gains	805
Available-for-sale, Gross Unrealized Losses	(255)	(84)
Securities available-for-sale	49,339	6,270
Securities held to maturity:
Held-to-maturity, Amortized Cost	6,544	8,780
Held-to-maturity, Gross Unrealized Gains	372	223
Fair Value	$ 6,916	$ 9,003
Number of securities in unrealized loss positions \| security	15	6
Corporate bonds
Securities available-for-sale:
Amortized Cost	$ 2,683
Available-for-sale, Gross Unrealized Gains	3
Available-for-sale, Gross Unrealized Losses	(5)
Securities available-for-sale	$ 2,681
Securities held to maturity:
Number of securities in unrealized loss positions \| security	2

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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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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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