Loans Receivable, Net - Impaired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, Recorded Investment	$ 13,037	$ 14,693
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, Unpaid Principal Balance	14,621	16,141
Impaired Financing Receivable, Related Allowance	315	361
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, Average Recorded Investment	13,842	16,082
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, Interest Income, Cash Basis Method	100	210
One-to-four family
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	5,439	3,416
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,065	2,091
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	6,862	4,210
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,065	2,215
Impaired Financing Receivable, Related Allowance	145	306
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	5,375	3,151
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	1,078	2,128
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	36	14
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	0	5
Multifamily
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	964	1,596
Impaired Financing Receivable, with Related Allowance, Recorded Investment	741	6
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	1,122	2,081
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	741	6
Impaired Financing Receivable, Related Allowance	75	6
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,340	1,747
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	248	1
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	34	6
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	0	0
Commercial real estate
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,539	993
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	2,502
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	1,539	993
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0	2,502
Impaired Financing Receivable, Related Allowance	0	6
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	2,075	1,774
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	541	1,427
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	28	17
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	0	0
Business
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	611	1,923
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,678	2,164
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	611	1,968
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	2,681	2,164
Impaired Financing Receivable, Related Allowance	95	41
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	827	3,667
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	2,358	2,187
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	0	142
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	2	26
Consumer
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	2
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0	2
Impaired Financing Receivable, Related Allowance	0	2
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0	1
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	$ 0	$ 0