Loans Receivable and Allowance for Loan and Lease Losses Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, Recorded Investment	$ 12,207		$ 12,207		$ 13,037
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, Unpaid Principal Balance	13,382		13,382		14,621
Impaired Financing Receivable, Related Allowance	193		193		315
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, Average Recorded Investment	12,182	$ 12,787	12,622	$ 14,401
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, Interest Income, Cash Basis Method	44	22	115	69
One-to-four family
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	4,508		4,508		5,439
Impaired Financing Receivable, with Related Allowance, Recorded Investment	935		935		1,065
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	5,663		5,663		6,862
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	930		930		1,065
Impaired Financing Receivable, Related Allowance	175		175		145
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	4,608	5,284	4,973	5,099
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	938	1,381	1,000	1,388
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	25	3	60	15
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	0	0	0	1
Multifamily
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	2,708		2,708		964
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0		0		741
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	2,708		2,708		1,122
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0		0		741
Impaired Financing Receivable, Related Allowance	0		0		75
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	2,518	1,068	1,836	1,379
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0	0	371	0
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	11	9	29	25
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		0	0	0
Commercial real estate
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	482		482		1,539
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	482		482		1,539
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	486	799	1,011	1,912
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	8	9	16	28
Business
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,774		1,774		611
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,800		1,800		2,678
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	1,795		1,795		611
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,804		1,804		2,681
Impaired Financing Receivable, Related Allowance	18		18		$ 95
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,204	1,632	1,192	2,020
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	2,428	2,623	2,239	2,603
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	0	0	6	0
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	$ 0	$ 1	$ 4	$ 0