Loans Receivable and Allowance for Loan and Lease Losses Credit Quality Indicators (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	$ 451,896	$ 477,753
Multifamily
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	99,292	104,865
Multifamily | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	98,339	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	953	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	128,797	142,304
Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	128,302	140,765
Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	0	0
Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	495	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	99,974	102,203
Business | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	91,519	93,886
Business | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,054	5,028
Business | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,401	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	118,871	123,092
One-to-four family | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	114,252	116,588
One-to-four family | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,619	6,504
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,962	5,289
Consumer | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	4,962	5,289
Consumer | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans, gross	$ 0	$ 0