Loans Receivable and Allowance for Loan and Lease Losses Credit Quality Indicators (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Mar. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	$ 427,407	$ 477,753
Multifamily
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	87,705	104,865
Multifamily | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	84,997	103,160
Multifamily | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Multifamily | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	2,708	1,705
Multifamily | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Multifamily | Loss
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	124,352	142,304
Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	123,234	140,765
Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	636	0
Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	482	1,539
Commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Commercial real estate | Loss
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Construction
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Construction | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Construction | Loss
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Business
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	99,118	102,203
Business | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	89,139	93,886
Business | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	5,751	5,028
Business | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,228	3,289
Business | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Business | Loss
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
One-to-four family
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	111,776	123,092
One-to-four family | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	108,015	116,588
One-to-four family | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	3,761	6,504
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,456	5,289
Consumer | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,411	5,289
Consumer | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	$ 45	$ 0