Loans Receivable and Allowance for Loan and Lease Losses Nonaccrual Loans (Details) - Nonperforming - USD ($) $ in Thousands	Sep. 30, 2017	Mar. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 8,850	$ 8,707
One-to-four family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	5,583	4,703
Multifamily
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	1,582	1,589
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	1,382	1,389
Business
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	303	1,026
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 0	$ 0