Loans Receivable, Net - Impaired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, Recorded Investment	$ 12,868	$ 8,450
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, Unpaid Principal Balance	13,718	9,314
Impaired Financing Receivable, Related Allowance	158	166
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, Average Recorded Investment	12,618	10,409
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, Interest Income, Cash Basis Method	192	160
One-to-four family
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	3,750	3,819
Impaired Financing Receivable, with Related Allowance, Recorded Investment	76	807
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	4,409	4,566
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	72	803
Impaired Financing Receivable, Related Allowance	32	156
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	4,119	4,153
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	503	868
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	64	65
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	369	375
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	369	376
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,791	1,795
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0	0
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	16	48
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	918	0
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	918	0
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	697	238
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	10	0
Business
Impaired Financing Receivable, Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	2,332	2,797
Impaired Financing Receivable, with Related Allowance, Recorded Investment	5,423	652
Impaired Financing Receivable, Unpaid Principal Balance
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	2,527	2,917
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	5,423	652
Impaired Financing Receivable, Related Allowance	126	10
Impaired Financing Receivable, Average Recorded Investment
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	2,153	2,385
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	3,355	970
Impaired Financing Receivable, Interest Income, Cash Basis Method
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	102	47
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	$ 0	$ 0