Loans Receivable, Net - Impaired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, Recorded Investment	$ 12,369	$ 13,037
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, Unpaid Principal Balance	13,567	14,621
Impaired Financing Receivable, Related Allowance	189	315
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, Average Recorded Investment	12,704	13,842
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, Interest Income, Cash Basis Method	182	100
One-to-four family
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	4,488	5,439
Impaired Financing Receivable, with Related Allowance, Recorded Investment	929	1,065
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	5,643	6,862
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	929	1,065
Impaired Financing Receivable, Related Allowance	171	145
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	4,964	5,375
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	997	1,078
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	96	36
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	0	0
Multifamily
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	3,214	964
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	741
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	3,214	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
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	2,089	1,340
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	371	248
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	42	34
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	476	1,539
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	0
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	476	1,539
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0	0
Impaired Financing Receivable, Related Allowance	0	0
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,007	2,075
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0	541
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	16	28
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	1,974	611
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,288	2,678
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	2,017	611
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	1,288	2,681
Impaired Financing Receivable, Related Allowance	18	95
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,293	827
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	1,983	2,358
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	18	0
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	10	2
Consumer
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	0
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0	0
Impaired Financing Receivable, Related Allowance	0	0
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0	0
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	$ 0	$ 0