Loans Receivable and Allowance for Loan and Lease Losses Credit Quality Indicators (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Mar. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	$ 431,369	$ 477,753
Multifamily
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	89,712	104,865
Multifamily | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	87,384	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	2,328	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	123,358	142,304
Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	122,230	140,765
Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	639	0
Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	489	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	98,732	102,203
Business | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	88,346	93,886
Business | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	5,774	5,028
Business | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,612	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	114,933	123,092
One-to-four family | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	110,631	116,588
One-to-four family | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,302	6,504
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,634	5,289
Consumer | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,634	5,289
Consumer | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	$ 0	$ 0