Loans Held for Investment - Schedule of Past Due Status of Loans Held for Investment, Gross (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans deemed uncollectible, period of delinquency	90 days	90 days
Current	$ 881,888	$ 898,947
30-89 Days Past Due	2	219
Non-Accrual	4,959	5,300
Total Loans Held for Investment, Gross	886,849	904,466	$ 925,005
Mortgage loans, Single-family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	283,862	293,326
30-89 Days Past Due	0	219
Non-Accrual	4,928	5,265
Total Loans Held for Investment, Gross	288,790	298,810	328,332
Mortgage Loans, Multi Family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	482,900	491,903
30-89 Days Past Due	0	0
Non-Accrual	0	0
Total Loans Held for Investment, Gross	482,900	491,903	479,597
Mortgage loans, Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	105,207	105,235
30-89 Days Past Due	0	0
Non-Accrual	0	0
Total Loans Held for Investment, Gross	105,207	105,235	110,652
Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	8,787	7,801
30-89 Days Past Due	0	0
Non-Accrual	0	0
Total Loans Held for Investment, Gross	8,787	7,801	5,912
Mortgage Loans Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	142	143
30-89 Days Past Due	0	0
Non-Accrual	0	0
Total Loans Held for Investment, Gross	142	143
Commercial business loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	892	445
30-89 Days Past Due	0	0
Non-Accrual	31	35
Total Loans Held for Investment, Gross	923	480	368
Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	98	94
30-89 Days Past Due	2	0
Non-Accrual	0	0
Total Loans Held for Investment, Gross	$ 100	$ 94	$ 144
Bankruptcy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans deemed uncollectible, period of delinquency	60 days
Troubled Debt Restructurings [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans deemed uncollectible, period of delinquency	90 days
Commercial Real Estate Or Second Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans deemed uncollectible, period of delinquency	120 days