Loans Receivable, Net - Impaired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, Recorded Investment	$ 8,450	$ 12,369
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, Unpaid Principal Balance	9,314	13,567
Impaired Financing Receivable, Related Allowance	166	189
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, Average Recorded Investment	10,409	12,704
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, Interest Income, Cash Basis Method	160	182
One-to-four family
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	3,819	4,488
Impaired Financing Receivable, with Related Allowance, Recorded Investment	807	929
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	4,566	5,643
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	803	929
Impaired Financing Receivable, Related Allowance	156	171
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	4,153	4,964
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	868	997
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	65	96
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	375	3,214
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	376	3,214
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,795	2,089
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0	371
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	48	42
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	0	476
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0	476
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	238	1,007
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	0	16
Business
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	2,797	1,974
Impaired Financing Receivable, with Related Allowance, Recorded Investment	652	1,288
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	2,917	2,017
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	652	1,288
Impaired Financing Receivable, Related Allowance	10	18
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	2,385	1,293
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	970	1,983
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	47	18
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	$ 0	$ 10