Mortgage-Backed Securities - Fair value and gross unrealized losses (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Mortgage-backed securities available for sale
Securities in a continuous unrealized loss position presented by length of time
Less than 12 Months, Fair Value	$ 9,127	$ 12,229
Less than 12 Months, Gross Unrealized Losses	(49)	(92)
12 Months or More, Fair Value	18,955	26,239
12 Months or More, Gross Unrealized Losses	(270)	(339)
Total, Fair Value	28,082	38,468
Total, Gross Unrealized Losses	(319)	(431)
Government pass-throughs, Ginnie Mae
Securities in a continuous unrealized loss position presented by length of time
Less than 12 Months, Fair Value	4,671	4,070
Less than 12 Months, Gross Unrealized Losses	(18)	(27)
12 Months or More, Fair Value	1,713	3,516
12 Months or More, Gross Unrealized Losses	(16)	(43)
Total, Fair Value	6,384	7,586
Total, Gross Unrealized Losses	(34)	(70)
Government pass-throughs, Freddie Mac
Securities in a continuous unrealized loss position presented by length of time
Less than 12 Months, Fair Value		5,537
Less than 12 Months, Gross Unrealized Losses		(34)
Total, Fair Value		5,537
Total, Gross Unrealized Losses		(34)
Private pass-throughs
Securities in a continuous unrealized loss position presented by length of time
Less than 12 Months, Fair Value		2,060
Less than 12 Months, Gross Unrealized Losses		(29)
12 Months or More, Fair Value	17,242	19,197
12 Months or More, Gross Unrealized Losses	(254)	(272)
Total, Fair Value	17,242	21,257
Total, Gross Unrealized Losses	(254)	(301)
Collateralized mortgage obligations
Securities in a continuous unrealized loss position presented by length of time
Less than 12 Months, Fair Value	4,456	562
Less than 12 Months, Gross Unrealized Losses	(31)	(2)
12 Months or More, Fair Value		3,526
12 Months or More, Gross Unrealized Losses		(24)
Total, Fair Value	4,456	4,088
Total, Gross Unrealized Losses	$ (31)	$ (26)