Loans Held for Investment - Schedule of Restructured Loans by Type, Net of Individually Evaluated Allowances (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) loan	Sep. 30, 2019 loan	Jun. 30, 2020 USD ($) loan
Financing Receivable, Impaired [Line Items]
Number of modified loans | loan	8		8
Restructured Loans, Allowance for Loan Losses	$ (90)		$ (112)
Restructured Loans, Unpaid Principal Balance	2,903		3,120
Restructured Loans, Related Charge-offs	(365)		(365)
Restructured Loans, Recorded Investment	2,538		2,755
Restructured loans, net investment	2,448		2,643
Mortgage loans, Single-family
Financing Receivable, Impaired [Line Items]
Restructured Loans, With Related Allowance, Unpaid Principal Balance	1,640		1,650
Restructured Loans, With Related Allowance, Related Charge-offs			0
Restructured Loans, With a Related Allowance, Recorded Investment	1,640		1,650
Restructured Loans, Allowance for Loan Losses	(86)		(108)
Restructured loans, with a related allowance, net investment	1,554		1,542
Restructured Loans, Without a Related Allowance, Unpaid Principal Balance	1,232		1,435
Restructured Loans, Without a Related Allowance, Related Charge-offs	(365)		(365)
Restructured Loans, Without a Related Allowance, Recorded Investment	867		1,070
Restructured Loans, Without a Related Allowance, Net Investment	867		1,070
Restructured Loans, Unpaid Principal Balance	2,872		3,085
Restructured Loans, Related Charge-offs	(365)		(365)
Restructured Loans, Recorded Investment	2,507		2,720
Restructured loans, net investment	2,421		2,612
Commercial business loans
Financing Receivable, Impaired [Line Items]
Restructured Loans, With Related Allowance, Unpaid Principal Balance	31		35
Restructured Loans, With Related Allowance, Related Charge-offs			0
Restructured Loans, With a Related Allowance, Recorded Investment	31		35
Restructured Loans, Allowance for Loan Losses	(4)		(4)
Restructured Loans, Unpaid Principal Balance	31		35
Restructured Loans, Related Charge-offs			0
Restructured Loans, Recorded Investment	31		35
Restructured loans, net investment	$ 27		$ 31
Substandard
Financing Receivable, Impaired [Line Items]
Number of modified loans | loan		2