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Loans - Activity in the allowance for loan losses by portfolio segment (Details) - USD ($)	3 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2020	Jun. 30, 2020
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	$ 1,774,757	$ 1,699,977	$ 1,589,531	$ 1,628,960
Charge-offs				(43,728)
Recoveries	342,954	74,780	1,981	4,299
Balance at end of year	2,117,711	1,774,757	1,591,512	1,589,531
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually evaluated for impairment						$ 1,055,383
Collectively evaluated for impairment					$ 2,117,711	644,594
Loans and Leases Receivable, Allowance	1,774,757	1,774,757	1,591,512	1,589,531	2,117,711	1,699,977
Loans - Individually evaluated for impairment					790,977	5,175,527
Loans - Collectively evaluated for impairment					124,644,766	113,697,830
Loans and Leases Receivable, Gross					125,435,743	118,873,357
Commercial real estate [Member] \| Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	661,379	274,997	241,510	249,631
Provisions	280,505	386,382	(22,168)	(8,121)
Balance at end of year	941,884	661,379	219,342	241,510
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Collectively evaluated for impairment					941,884	274,997
Loans and Leases Receivable, Allowance	941,884	274,997	219,342	241,510	941,884	274,997
Loans - Individually evaluated for impairment					230,331	688,616
Loans - Collectively evaluated for impairment					47,324,480	40,087,474
Loans and Leases Receivable, Gross					47,554,811	40,776,090
Commercial [Member] \| Commercial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	113,232	1,021,083	806,196	899,618
Recoveries	341,388
Provisions	(344,174)	(907,851)	44,886	(93,422)
Balance at end of year	110,446	113,232	851,082	806,196
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually evaluated for impairment						274,997
Collectively evaluated for impairment					110,446	48,485
Loans and Leases Receivable, Allowance	110,446	1,021,083	851,082	806,196	110,446	1,021,083
Loans - Individually evaluated for impairment						2,249,492
Loans - Collectively evaluated for impairment					11,017,967	10,789,768
Loans and Leases Receivable, Gross					11,017,967	13,039,260
Commercial [Member] \| Construction
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	127,596	43,858	2,583	1,643
Recoveries		73,128
Provisions	2,444	10,610	527	940
Balance at end of year	130,040	127,596	3,110	2,583
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Collectively evaluated for impairment					130,040	43,858
Loans and Leases Receivable, Allowance	130,040	127,596	3,110	2,583	130,040	43,858
Loans - Collectively evaluated for impairment					10,080,584	11,103,198
Loans and Leases Receivable, Gross					10,080,584	11,103,198
Residential [Member] \| One-to-four-family residential
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	623,165	339,449	381,163	333,660
Charge-offs				(43,728)
Provisions	(47,961)	283,716	(26,928)	91,231
Balance at end of year	575,204	623,165	354,235	381,163
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually evaluated for impairment						82,785
Collectively evaluated for impairment					575,204	256,664
Loans and Leases Receivable, Allowance	575,204	339,449	354,235	381,163	575,204	339,449
Loans - Individually evaluated for impairment					470,318	2,237,419
Loans - Collectively evaluated for impairment					42,803,943	39,484,327
Loans and Leases Receivable, Gross					43,274,261	41,721,746
Residential [Member] \| Multi-family real estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	62,572	10,057
Provisions	23,163	52,515
Balance at end of year	85,735	62,572
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Collectively evaluated for impairment					85,735	10,057
Loans and Leases Receivable, Allowance	85,735	62,572			85,735	10,057
Loans - Individually evaluated for impairment					90,328
Loans - Collectively evaluated for impairment					11,431,363	9,578,554
Loans and Leases Receivable, Gross					11,521,691	9,578,554
Consumer Loans [Member] \| Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	12,881	2,003	5,773	13,255
Recoveries	1,566	1,652	1,981	4,299
Provisions	(3,893)	9,226	(2,172)	(11,781)
Balance at end of year	10,554	12,881	5,582	5,773
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Collectively evaluated for impairment					10,554	2,003
Loans and Leases Receivable, Allowance	10,554	12,881	5,582	5,773	10,554	2,003
Loans - Collectively evaluated for impairment					1,986,429	2,654,509
Loans and Leases Receivable, Gross					1,986,429	2,654,509
Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	173,932	8,530	152,306	131,153
Provisions	89,916	165,402	5,855	21,153
Balance at end of year	263,848	173,932	158,161	152,306
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Collectively evaluated for impairment					263,848	8,530
Loans and Leases Receivable, Allowance	$ 263,848	$ 173,932	$ 158,161	$ 152,306	$ 263,848	$ 8,530