Past Due Financing Receivables (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Mar. 31, 2020
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	$ 22,076	$ 13,913
Financing Receivable, Not Past Due	446,517	414,819
Loans, gross	468,593	428,732
Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	12,531	9,984
Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	3,245	4
Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	6,300	3,925
One-to-four family
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	4,082	4,612
Financing Receivable, Not Past Due	78,965	102,916
Loans, gross	83,047	107,528
One-to-four family | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	882	1,410
One-to-four family | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	247	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	2,953	3,202
Multifamily
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	9,409	490
Financing Receivable, Not Past Due	98,314	89,397
Loans, gross	107,723	89,887
Multifamily | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	8,333	490
Multifamily | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,076	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	6,181	6,621
Financing Receivable, Not Past Due	141,339	135,789
Loans, gross	147,520	142,410
Commercial real estate | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	2,671	6,621
Commercial real estate | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,419	0
Commercial real estate | Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	2,091	0
Business
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	2,297	2,063
Financing Receivable, Not Past Due	125,251	83,596
Loans, gross	127,548	85,659
Business | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	620	1,360
Business | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	421	3
Business | Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,256	700
Consumer
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	107	127
Financing Receivable, Not Past Due	2,648	3,121
Loans, gross	2,755	3,248
Consumer | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	25	103
Consumer | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	82	1
Consumer | Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	$ 0	$ 23