Loans Receivable and Allowance for Loan and Lease Losses Credit Quality Indicators (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	$ 496,708	$ 545,552	$ 532,818
Multifamily
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	75,805	88,750	71,924
Multifamily | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	74,160	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	1,645	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	219,939	242,818	250,810
Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	219,431	238,552
Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	771
Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	508	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	4,962
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	69,357	65,114	66,200
Business | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	60,982	58,555
Business | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	3,764	133
Business | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,611	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	125,678	134,927	138,620
One-to-four family | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	121,238	131,028
One-to-four family | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,440	3,899
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	5,929	8,994	$ 302
Consumer | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	5,928	8,992
Consumer | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	$ 1	$ 2