Loans Receivable and Allowance for Loan and Lease Losses Credit Quality Indicators (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Mar. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	$ 433,284	$ 428,828
Multifamily
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	82,823	86,886
Multifamily | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	80,390	83,672
Multifamily | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Multifamily | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	2,433	3,214
Multifamily | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Multifamily | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	137,451	131,292
Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	136,826	128,319
Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	625	2,497
Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	476
Commercial real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Commercial real estate | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Business
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	90,816	96,661
Business | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	84,496	90,336
Business | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	3,981	2,425
Business | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	2,339	3,900
Business | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Business | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
One-to-four family
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	118,502	109,926
One-to-four family | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	114,749	106,531
One-to-four family | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	3,753	3,395
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	3,692	4,063
Consumer | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	3,657	4,063
Consumer | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	$ 35	$ 0