Loans Receivable and Allowance For Loan Losses - Financing Receivables, Related Allowance Recorded and No Related Allowance Recorder (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Unpaid Principal Balance, with no related allowance recorded	$ 2,685	$ 1,727
Unpaid Principal Balance, with related allowance recorded	537	2,516
Impaired Financing Receivable, Unpaid Principal Balance, Total	3,222	4,243
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment, with no related allowance recorded	2,592	1,378
Recorded Investment, with related allowance recorded	536	2,516
Recorded Investment	3,128	3,894
Impaired Financing Receivable Related Allowance Abstract
Related Allowance, with related allowance recorded	182	975
Related Allowance	182	975
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment, with no related allowance recorded	1,980	1,554
Average Recorded Investment, with related allowance recorded	582	2,125
Impaired Financing Receivable, Average Recorded Investment	2,562	3,679
Impaired Financing Receivable, Interest Income [Abstract]
Interest Income Recognized, with no related allowance recorded	95	30
Interest Income Recognized, with related allowance recorded	48	124
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	143	154
Commercial
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Unpaid Principal Balance, with no related allowance recorded	1,097
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment, with no related allowance recorded	1,086
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment, with no related allowance recorded	90
Impaired Financing Receivable, Interest Income [Abstract]
Interest Income Recognized, with no related allowance recorded	56
Home equity.
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Unpaid Principal Balance, with no related allowance recorded	278	305
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment, with no related allowance recorded	225	229
Impaired Financing Receivable Related Allowance Abstract
Related Allowance, with no related allowance recorded	0	0
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment, with no related allowance recorded	206	404
Impaired Financing Receivable, Interest Income [Abstract]
Interest Income Recognized, with no related allowance recorded	3	8
One-to-four-family
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Unpaid Principal Balance, with no related allowance recorded	1,293	991
Unpaid Principal Balance, with related allowance recorded	61	834
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment, with no related allowance recorded	1,264	718
Recorded Investment, with related allowance recorded	60	834
Impaired Financing Receivable Related Allowance Abstract
Related Allowance, with related allowance recorded	15	125
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment, with no related allowance recorded	1,500	719
Average Recorded Investment, with related allowance recorded	5	1,030
Impaired Financing Receivable, Interest Income [Abstract]
Interest Income Recognized, with no related allowance recorded	34	0
Interest Income Recognized, with related allowance recorded	5	28
Indirect home improvement
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Unpaid Principal Balance, with related allowance recorded	451	367
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment, with related allowance recorded	451	367
Impaired Financing Receivable Related Allowance Abstract
Related Allowance, with related allowance recorded	158	128
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment, with related allowance recorded	427	295
Impaired Financing Receivable, Interest Income [Abstract]
Interest Income Recognized, with related allowance recorded	41	32
Solar
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Unpaid Principal Balance, with related allowance recorded	17	41
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment, with related allowance recorded	17	41
Impaired Financing Receivable Related Allowance Abstract
Related Allowance, with related allowance recorded	6	15
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment, with related allowance recorded	36	31
Impaired Financing Receivable, Interest Income [Abstract]
Interest Income Recognized, with related allowance recorded	1	3
Marine
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Unpaid Principal Balance, with related allowance recorded		18
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment, with related allowance recorded		18
Impaired Financing Receivable Related Allowance Abstract
Related Allowance, with related allowance recorded		6
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment, with related allowance recorded	13	11
Impaired Financing Receivable, Interest Income [Abstract]
Interest Income Recognized, with related allowance recorded		2
Other consumer loans
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Unpaid Principal Balance, with no related allowance recorded	17
Unpaid Principal Balance, with related allowance recorded	8
Impaired Financing Receivable, Unpaid Principal Balance, Total		2
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment, with no related allowance recorded	17
Recorded Investment, with related allowance recorded	8
Recorded Investment		2
Impaired Financing Receivable Related Allowance Abstract
Related Allowance, with related allowance recorded	3
Related Allowance		1
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment, with no related allowance recorded	4
Average Recorded Investment, with related allowance recorded	5	1
Impaired Financing Receivable, Interest Income [Abstract]
Interest Income Recognized, with no related allowance recorded	2
Interest Income Recognized, with related allowance recorded	1
Commercial and industrial
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Unpaid Principal Balance, with no related allowance recorded		431
Unpaid Principal Balance, with related allowance recorded		1,254
Impaired Financing Receivable, Recorded Investment [Abstract]
Recorded Investment, with no related allowance recorded		431
Recorded Investment, with related allowance recorded		1,254
Impaired Financing Receivable Related Allowance Abstract
Related Allowance, with related allowance recorded		700
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Average Recorded Investment, with no related allowance recorded	180	431
Average Recorded Investment, with related allowance recorded	$ 96	757
Impaired Financing Receivable, Interest Income [Abstract]
Interest Income Recognized, with no related allowance recorded		22
Interest Income Recognized, with related allowance recorded		$ 59

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-Topic 310
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-Section 50
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