Loans Receivable and Allowance for Loan and Lease Losses Past Due Financing Receivables (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Mar. 31, 2019
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	$ 6,940	$ 11,625
Financing Receivable, Not Past Due	426,344	417,203
Loans, gross	433,284	428,828
Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	136	5,395
Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,063	53
Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	5,741	6,177
One-to-four family
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	3,644	5,222
Financing Receivable, Not Past Due	114,858	104,704
Loans, gross	118,502	109,926
One-to-four family | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	1,827
One-to-four family | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	623	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	3,021	3,395
Multifamily
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	2,053	4,698
Financing Receivable, Not Past Due	80,770	82,188
Loans, gross	82,823	86,886
Multifamily | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	2,580
Multifamily | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
Multifamily | Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	2,053	2,118
Commercial real estate
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	121
Financing Receivable, Not Past Due	137,451	131,171
Loans, gross	137,451	131,292
Commercial real estate | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	121
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	0	0
Business
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,121	1,379
Financing Receivable, Not Past Due	89,695	95,282
Loans, gross	90,816	96,661
Business | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	14	780
Business | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	440	0
Business | Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	667	599
Consumer
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	122	205
Financing Receivable, Not Past Due	3,570	3,858
Loans, gross	3,692	4,063
Consumer | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	122	87
Consumer | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	53
Consumer | Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	$ 0	$ 65