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Loans - Major classifications of loans (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 501,909		$ 517,467
Loans in process	(2,876)		(4,895)
Unearned loan origination fees	(641)		(448)
Allowance for loan losses	(3,587)	$ (3,585)	(3,519)	$ (2,988)	$ (3,209)	$ (3,209)
Net Loans	$ 494,805		$ 508,605
Percentage of loans	100.00%		100.00%
Residential real estate \| 1-4 Family
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 325,728		$ 345,915
Allowance for loan losses	$ (1,571)	(1,590)	$ (1,483)	(1,828)	(1,872)	(1,501)
Percentage of loans	64.90%		66.85%
Residential real estate \| Home equity and HELOCs
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 45,093		$ 47,054
Allowance for loan losses	$ (160)	(150)	$ (166)	(130)	(137)	(122)
Percentage of loans	8.99%		9.10%
Residential real estate \| Construction Residential
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 13,581		$ 15,799
Allowance for loan losses	$ (463)	(461)	$ (526)	(159)	(203)	(321)
Percentage of loans	2.71%		3.05%
Commercial real estate \| Multi-family
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 12,223		$ 14,964
Allowance for loan losses	$ (161)	(121)	$ (123)	(106)	(113)	(71)
Percentage of loans	2.43%		2.89%
Commercial real estate \| Commercial non-residential
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 89,952		$ 76,707
Allowance for loan losses	$ (851)	(780)	$ (727)	(435)	(444)	(708)
Percentage of loans	17.93%		14.83%
Commercial real estate \| Construction and Land
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 5,818		$ 6,690
Allowance for loan losses	$ (334)	(436)	$ (396)	(109)	(92)	(121)
Percentage of loans	1.16%		1.29%
Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 6,027		$ 6,438
Allowance for loan losses	$ (32)	(32)	$ (83)	(42)	(40)	(95)
Percentage of loans	1.20%		1.24%
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total Loans	$ 3,487		$ 3,900
Allowance for loan losses	$ (15)	$ (15)	$ (15)	$ (15)	$ (15)	$ (3)
Percentage of loans	0.68%		0.75%