Past Due Financing Receivables (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 31, 2020
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	$ 19,182	$ 13,913
Financing Receivable, Not Past Due	445,017	414,819
Loans, gross	464,199	428,732
Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	3,448	9,984
Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	5,578	4
Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	10,156	3,925
One-to-four family
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	3,756	4,612
Financing Receivable, Not Past Due	83,813	102,916
Loans, gross	87,569	107,528
One-to-four family | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	799	1,410
One-to-four family | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
One-to-four family | Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	2,957	3,202
Multifamily
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,212	490
Financing Receivable, Not Past Due	95,950	89,397
Loans, gross	97,162	89,887
Multifamily | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	729	490
Multifamily | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	483	0
Multifamily | Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
Commercial real estate
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	6,853	6,621
Financing Receivable, Not Past Due	141,098	135,789
Loans, gross	147,951	142,410
Commercial real estate | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	936	6,621
Commercial real estate | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
Commercial real estate | Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	5,917	0
Business
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	7,084	2,063
Financing Receivable, Not Past Due	121,557	83,596
Loans, gross	128,641	85,659
Business | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	808	1,360
Business | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	4,994	3
Business | Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,282	700
Consumer
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	277	127
Financing Receivable, Not Past Due	2,599	3,121
Loans, gross	2,876	3,248
Consumer | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	176	103
Consumer | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	101	1
Consumer | Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	$ 0	$ 23