Loans Receivable and Allowance for Loan and Lease Losses Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, Recorded Investment	$ 12,395		$ 13,037
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, Unpaid Principal Balance	14,377		14,621
Impaired Financing Receivable, Related Allowance	761		315
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, Average Recorded Investment	12,718	$ 15,989
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, Interest Income, Cash Basis Method	56	34
One-to-four family
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	4,916		5,439
Impaired Financing Receivable, with Related Allowance, Recorded Investment	833		1,065
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	6,844		6,862
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	828		1,065
Impaired Financing Receivable, Related Allowance	235		145
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	5,178	4,723
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	949	1,563
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	29	6
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		0
Multifamily
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	2,436		964
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0		741
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	2,495		1,122
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0		741
Impaired Financing Receivable, Related Allowance	0		75
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,700	1,592
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	9	9
Commercial real estate
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	495		1,539
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	495		1,539
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,017	1,391
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0	1,624
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	8	19
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		0
Business
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	670		611
Impaired Financing Receivable, with Related Allowance, Recorded Investment	3,045		2,678
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	670		611
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	3,045		2,681
Impaired Financing Receivable, Related Allowance	526		$ 95
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	641	1,387
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	2,862	3,709
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	6	0
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	$ 4	$ 0