Loans Receivable and Allowance for Loan and Lease Losses Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, Recorded Investment	$ 12,982		$ 12,982		$ 14,693
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, Unpaid Principal Balance	14,841		14,841		16,141
Impaired Financing Receivable, Related Allowance	344		344		361
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, Average Recorded Investment	13,094	$ 16,415	14,542	$ 16,672
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, Interest Income, Cash Basis Method	22	13	69	192
One-to-four family
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	5,073		5,073		3,416
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,379		1,379		2,091
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	6,366		6,366		4,210
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,510		1,510		2,215
Impaired Financing Receivable, Related Allowance	151		151		306
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	5,284	3,220	5,099	2,927
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	1,381	2,163	1,388	2,174
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	3	0	15	7
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	0	4	0	5
Multifamily
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	839		839		1,596
Impaired Financing Receivable, with Related Allowance, Recorded Investment	806		806		6
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	1,188		1,188		2,081
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	806		806		6
Impaired Financing Receivable, Related Allowance	136		136		6
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,068	1,608	1,379	1,689
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	9	0	25	6
Commercial real estate
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	508		508		993
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0		0		2,502
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	508		508		993
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0		0		2,502
Impaired Financing Receivable, Related Allowance	0		0		6
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	799	1,952	1,912	1,969
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0	1,429	0	1,431
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	9	9	28	9
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	0	0	0	0
Business
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,788		1,788		1,923
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,589		2,589		2,164
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	1,861		1,861		1,968
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	2,602		2,602		2,164
Impaired Financing Receivable, Related Allowance	57		57		41
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,632	3,459	2,020	3,842
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	2,623	2,581	2,603	2,639
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	0	0	0	128
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	1	0	1	37
Consumer
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0		0		2
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0		0		2
Impaired Financing Receivable, Related Allowance	0		0		$ 2
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0	3	0	1
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	$ 0	$ 0	$ 0	$ 0