Loans Receivable and Allowance for Loan and Lease Losses Credit Quality Indicators (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	$ 518,543	$ 545,552	$ 528,755
Multifamily
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	81,765	88,750	74,751
Multifamily | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	80,183	87,148
Multifamily | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Multifamily | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	1,582	1,082
Multifamily | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	520
Multifamily | Loss
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	224,919	242,818	251,988
Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	222,783	238,552
Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	754	771
Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	1,382	3,495
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	4,949	4,975
Construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	4,949
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	72,991	65,114	66,118
Business | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	68,147	58,555
Business | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	390	133
Business | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,454	6,426
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	130,480	134,927	130,673
One-to-four family | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	125,057	131,028
One-to-four family | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	5,423	3,899
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	8,388	8,994	$ 250
Consumer | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	8,388	8,992
Consumer | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	$ 0	$ 2