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Loans and Allowance for Loan Losses - Allowance for Loan Losses and Recorded Investment in Loans Based on Portfolio Segment and Impairment Method (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021
Allowance for loan losses:
Balance, beginning of year	$ 6,599	$ 6,234	$ 6,234
Provision charged to expense	(127)	315	844
Losses charged off	(10)	(57)	(513)
Recoveries	8	14	34
Balance, end of period	6,470	6,506	6,599
Ending balance: individually evaluated for impairment	0	0	0
Ending balance: collectively evaluated for impairment	6,470	6,506	6,599
Loans:
Ending balance	512,984	525,033	520,526
Ending balance: individually evaluated for impairment	1,129	1,336	1,298
Ending balance: collectively evaluated for impairment	511,855	523,697	519,228
One- to four-family [Member]
Allowance for loan losses:
Balance, beginning of year	967	1,044	1,044
Provision charged to expense	6	4	(64)
Losses charged off	0	(15)	(15)
Recoveries	1	0	2
Balance, end of period	974	1,033	967
Ending balance: individually evaluated for impairment	0	0	0
Ending balance: collectively evaluated for impairment	974	1,033	967
Loans:
Ending balance	117,854	125,574	117,435
Ending balance: individually evaluated for impairment	1,086	1,277	1,252
Ending balance: collectively evaluated for impairment	116,768	124,297	116,183
Multi-family [Member]
Allowance for loan losses:
Balance, beginning of year	1,674	1,514	1,514
Provision charged to expense	(112)	227	160
Losses charged off	0	0	0
Recoveries	0	0	0
Balance, end of period	1,562	1,741	1,674
Ending balance: individually evaluated for impairment	0	0	0
Ending balance: collectively evaluated for impairment	1,562	1,741	1,674
Loans:
Ending balance	97,211	106,886	104,433
Ending balance: individually evaluated for impairment	0	0	0
Ending balance: collectively evaluated for impairment	97,211	106,886	104,433
Home equity lines of credit [Member]
Allowance for loan losses:
Balance, beginning of year	67	87	87
Provision charged to expense	(4)	(5)	(20)
Losses charged off	0	0	0
Recoveries	0	0	0
Balance, end of period	63	82	67
Ending balance: individually evaluated for impairment	0	0	0
Ending balance: collectively evaluated for impairment	63	82	67
Loans:
Ending balance	6,274	8,147	6,688
Ending balance: individually evaluated for impairment	0	0	0
Ending balance: collectively evaluated for impairment	6,274	8,147	6,688
Construction [Member]
Allowance for loan losses:
Balance, beginning of year	258	240	240
Provision charged to expense	63	(155)	18
Losses charged off	0	0	0
Recoveries	0	0	0
Balance, end of period	321	85	258
Ending balance: individually evaluated for impairment	0	0	0
Ending balance: collectively evaluated for impairment	321	85	258
Loans:
Ending balance	31,209	10,050	25,345
Ending balance: individually evaluated for impairment	0	0	0
Ending balance: collectively evaluated for impairment	31,209	10,050	25,345
Commercial [Member]
Allowance for loan losses:
Balance, beginning of year	1,831	1,706	1,706
Provision charged to expense	85	168	125
Losses charged off	0	0	0
Recoveries	0	0	0
Balance, end of period	1,916	1,874	1,831
Ending balance: individually evaluated for impairment	0	0	0
Ending balance: collectively evaluated for impairment	1,916	1,874	1,831
Loans:
Ending balance	163,859	157,096	155,884
Ending balance: individually evaluated for impairment	0	0	0
Ending balance: collectively evaluated for impairment	163,859	157,096	155,884
Commercial [Member]
Allowance for loan losses:
Balance, beginning of year	1,740	1,583	1,583
Provision charged to expense	(174)	61	611
Losses charged off	0	(29)	(473)
Recoveries	5	9	19
Balance, end of period	1,571	1,624	1,740
Ending balance: individually evaluated for impairment	0	0	0
Ending balance: collectively evaluated for impairment	1,571	1,624	1,740
Loans:
Ending balance	88,962	109,182	103,088
Ending balance: individually evaluated for impairment	43	55	46
Ending balance: collectively evaluated for impairment	88,919	109,127	103,042
Consumer [Member]
Allowance for loan losses:
Balance, beginning of year	62	60	60
Provision charged to expense	9	15	14
Losses charged off	(10)	(13)	(25)
Recoveries	2	5	13
Balance, end of period	63	67	62
Ending balance: individually evaluated for impairment	0	0	0
Ending balance: collectively evaluated for impairment	63	67	62
Loans:
Ending balance	7,615	8,098	7,653
Ending balance: individually evaluated for impairment	0	4	0
Ending balance: collectively evaluated for impairment	$ 7,615	$ 8,094	$ 7,653

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