Loans Receivable and Allowance for Loan and Lease Losses Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2017
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, Recorded Investment	$ 14,548		$ 14,548		$ 14,693
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, Unpaid Principal Balance	16,616		16,616		16,141
Impaired Financing Receivable, Related Allowance	277		277		361
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, Average Recorded Investment	14,632	$ 16,133	15,313	$ 15,954
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, Interest Income, Cash Basis Method	12	9	46	179
One-to-four family
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	6,020		6,020		3,416
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,079		1,079		2,091
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	7,509		7,509		4,210
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,079		1,079		2,215
Impaired Financing Receivable, Related Allowance	148		148		306
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	5,428	3,183	5,313	3,081
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	1,081	1,712	1,085	1,717
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	6	0	12	7
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	1,524		1,524		1,596
Impaired Financing Receivable, with Related Allowance, Recorded Investment	58		58		6
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	2,009		2,009		2,081
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	58		58		6
Impaired Financing Receivable, Related Allowance	61		61		6
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,528	1,703	1,533	1,729
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	6	4	15	6
Commercial real estate
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,382		1,382		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	1,382		1,382		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	1,923	1,971	2,469	1,978
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0	882	0	883
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	0	0	19	0
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	1,928		1,928		1,923
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,557		2,557		2,164
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	2,001		2,001		1,968
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	2,578		2,578		2,164
Impaired Financing Receivable, Related Allowance	68		68		41
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	2,037	3,577	2,262	3,477
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	2,577	3,105	2,593	3,089
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	0	4	0	128
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	0	1	0	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	0	0	0
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	$ 0	$ 0	$ 0	$ 0