Loans and Allowance for Loan Losses - Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Loans and Allowance for Loan Losses
Loans with no related allowance recorded, Recorded Investment	$ 7,902		$ 7,902		$ 10,317
Loans with no related allowance recorded, Unpaid Principal Balance	8,961		8,961		10,915
Loans with no related allowance recorded, Related Allowance	0		0		0
Loans with no related allowance recorded, Average Recorded Investment	11,358	$ 11,512	11,196	$ 11,195
Loans with no related allowance recorded, Interest Income Recognized	21	81	55	173
Loans with an allowance recorded, Recorded Investment	5,523		5,523		6,367
Loans with an allowance recorded, Unpaid Principal Balance	6,255		6,255		6,798
Loans with an allowance recorded, Related Allowance	574		574		1,443
Loans with an allowance recorded, Average Recorded Investment	4,268	5,789	5,112	4,793
Loans with an allowance recorded, Interest Income Recognized	0	0
Total, Recorded Investment	13,425		13,425		16,684
Total, Unpaid Principal Balance	15,216		15,216		17,713
Total, Related Allowance	574		574		1,443
Total, Average Recorded Investment	15,606	17,301	16,308	15,988
Total, Interest Income Recognized	21	81	55	173
Residential real estate [Member]
Loans and Allowance for Loan Losses
Loans with no related allowance recorded, Recorded Investment	3,491		3,491		5,185
Loans with no related allowance recorded, Unpaid Principal Balance	4,115		4,115		5,697
Loans with no related allowance recorded, Related Allowance	0		0		0
Loans with no related allowance recorded, Average Recorded Investment	4,503	5,338	4,899	5,215
Loans with no related allowance recorded, Interest Income Recognized	11	34	38	61
Loans with an allowance recorded, Recorded Investment	172		172		174
Loans with an allowance recorded, Unpaid Principal Balance	175		175		175
Loans with an allowance recorded, Related Allowance	27		27		30
Loans with an allowance recorded, Average Recorded Investment	88	55	117	39
Loans with an allowance recorded, Interest Income Recognized	0	0
Total, Recorded Investment	3,663		3,663		5,359
Total, Unpaid Principal Balance	4,290		4,290		5,872
Total, Related Allowance	27		27		30
Total, Average Recorded Investment	4,591	5,393	5,016	5,254
Total, Interest Income Recognized	11	34	38	61
Commercial real estate [Member]
Loans and Allowance for Loan Losses
Loans with no related allowance recorded, Recorded Investment	1,088		1,088		1,134
Loans with no related allowance recorded, Unpaid Principal Balance	1,154		1,154		1,185
Loans with no related allowance recorded, Related Allowance	0		0		0
Loans with no related allowance recorded, Average Recorded Investment	1,161	4,659	1,169	4,861
Loans with no related allowance recorded, Interest Income Recognized	9	35	15	80
Loans with an allowance recorded, Recorded Investment	0		0		0
Loans with an allowance recorded, Unpaid Principal Balance	0		0		0
Loans with an allowance recorded, Related Allowance	0		0		0
Loans with an allowance recorded, Average Recorded Investment	0	50		33
Loans with an allowance recorded, Interest Income Recognized	0	0
Total, Recorded Investment	1,088		1,088		1,134
Total, Unpaid Principal Balance	1,154		1,154		1,185
Total, Related Allowance	0		0		0
Total, Average Recorded Investment	1,161	4,709	1,169	4,894
Total, Interest Income Recognized	9	35	15	80
Single tenant net lease
Loans and Allowance for Loan Losses
Loans with no related allowance recorded, Recorded Investment	0		0		0
Loans with no related allowance recorded, Unpaid Principal Balance	0		0		0
Loans with no related allowance recorded, Related Allowance	0		0		0
Loans with no related allowance recorded, Average Recorded Investment	0	0	0
Loans with no related allowance recorded, Interest Income Recognized	0	0	0
Loans with an allowance recorded, Recorded Investment	0		0		0
Loans with an allowance recorded, Unpaid Principal Balance	0		0		0
Loans with an allowance recorded, Related Allowance	0		0		0
Loans with an allowance recorded, Average Recorded Investment	0	0
Loans with an allowance recorded, Interest Income Recognized	0	0
Total, Recorded Investment	0		0		0
Total, Unpaid Principal Balance	0		0		0
Total, Related Allowance	0		0		0
Total, Average Recorded Investment	0	0
Total, Interest Income Recognized	0	0
SBA commercial real estate
Loans and Allowance for Loan Losses
Loans with no related allowance recorded, Recorded Investment	593		593		1,245
Loans with no related allowance recorded, Unpaid Principal Balance	768		768		1,178
Loans with no related allowance recorded, Related Allowance	0		0		0
Loans with no related allowance recorded, Average Recorded Investment	2,755	740	2,229	541
Loans with no related allowance recorded, Interest Income Recognized	0	12	0	29
Loans with an allowance recorded, Recorded Investment	4,793		4,793		5,682
Loans with an allowance recorded, Unpaid Principal Balance	5,415		5,415		6,086
Loans with an allowance recorded, Related Allowance	501		501		1,366
Loans with an allowance recorded, Average Recorded Investment	3,548	4,561	4,394	3,920
Loans with an allowance recorded, Interest Income Recognized	0	0
Total, Recorded Investment	5,386		5,386		6,927
Total, Unpaid Principal Balance	6,183		6,183		7,264
Total, Related Allowance	501		501		1,366
Total, Average Recorded Investment	6,303	5,301	6,623	4,461
Total, Interest Income Recognized	0	12		29
Multifamily
Loans and Allowance for Loan Losses
Loans with no related allowance recorded, Recorded Investment	648		648		698
Loans with no related allowance recorded, Unpaid Principal Balance	693		693		700
Loans with no related allowance recorded, Related Allowance	0		0		0
Loans with no related allowance recorded, Average Recorded Investment	693	352	696	234
Loans with no related allowance recorded, Interest Income Recognized	0	0	0
Loans with an allowance recorded, Recorded Investment	0		0		0
Loans with an allowance recorded, Unpaid Principal Balance	0		0		0
Loans with an allowance recorded, Related Allowance	0		0		0
Loans with an allowance recorded, Average Recorded Investment	0	0
Loans with an allowance recorded, Interest Income Recognized	0	0
Total, Recorded Investment	648		648		698
Total, Unpaid Principal Balance	693		693		700
Total, Related Allowance	0		0		0
Total, Average Recorded Investment	693	352	696	234
Total, Interest Income Recognized	0	0
Residential Construction
Loans and Allowance for Loan Losses
Loans with no related allowance recorded, Recorded Investment	0		0		0
Loans with no related allowance recorded, Unpaid Principal Balance	0		0		0
Loans with no related allowance recorded, Related Allowance	0		0		0
Loans with no related allowance recorded, Average Recorded Investment	0	0	0
Loans with no related allowance recorded, Interest Income Recognized	0	0	0	0
Loans with an allowance recorded, Recorded Investment	0		0		0
Loans with an allowance recorded, Unpaid Principal Balance	0		0		0
Loans with an allowance recorded, Related Allowance	0	0	0	0	0
Loans with an allowance recorded, Average Recorded Investment	0	0
Loans with an allowance recorded, Interest Income Recognized	0	0
Total, Recorded Investment	0		0		0
Total, Unpaid Principal Balance	0		0		0
Total, Related Allowance	0	0	0	0	0
Total, Average Recorded Investment		0
Total, Interest Income Recognized	0
Commercial Construction
Loans and Allowance for Loan Losses
Loans with no related allowance recorded, Recorded Investment	0		0		0
Loans with no related allowance recorded, Unpaid Principal Balance	0		0		0
Loans with no related allowance recorded, Related Allowance	0		0		0
Loans with no related allowance recorded, Average Recorded Investment	0	0	0
Loans with no related allowance recorded, Interest Income Recognized	0	0	0
Loans with an allowance recorded, Recorded Investment	0		0		0
Loans with an allowance recorded, Unpaid Principal Balance	0		0		0
Loans with an allowance recorded, Related Allowance	0	0	0	0	0
Loans with an allowance recorded, Average Recorded Investment	0	0
Loans with an allowance recorded, Interest Income Recognized	0	0
Total, Recorded Investment	0		0		0
Total, Unpaid Principal Balance					0
Total, Related Allowance	0	0	0	0	0
Total, Average Recorded Investment	0	0
Land and land development
Loans and Allowance for Loan Losses
Loans with no related allowance recorded, Recorded Investment	4		4		2
Loans with no related allowance recorded, Unpaid Principal Balance	1		1		1
Loans with no related allowance recorded, Related Allowance	0		0		0
Loans with no related allowance recorded, Average Recorded Investment	1	1	1
Loans with no related allowance recorded, Interest Income Recognized	0	0	0
Loans with an allowance recorded, Recorded Investment	0		0		0
Loans with an allowance recorded, Unpaid Principal Balance	0		0		0
Loans with an allowance recorded, Related Allowance	0		0		0
Loans with an allowance recorded, Average Recorded Investment	0	0
Loans with an allowance recorded, Interest Income Recognized	0	0
Total, Recorded Investment	4		4		2
Total, Unpaid Principal Balance	1		1		1
Total, Related Allowance	0		0		0
Total, Average Recorded Investment	1	1	1
Total, Interest Income Recognized	0	0
Commercial Business
Loans and Allowance for Loan Losses
Loans with no related allowance recorded, Recorded Investment	1,701		1,701		1,670
Loans with no related allowance recorded, Unpaid Principal Balance	1,758		1,758		1,675
Loans with no related allowance recorded, Related Allowance	0		0		0
Loans with no related allowance recorded, Average Recorded Investment	1,712	139	1,700	128
Loans with no related allowance recorded, Interest Income Recognized	1	0	1	1
Loans with an allowance recorded, Recorded Investment	5		5		0
Loans with an allowance recorded, Unpaid Principal Balance	5		5		0
Loans with an allowance recorded, Related Allowance	5		5		0
Loans with an allowance recorded, Average Recorded Investment	2	783	2	522
Loans with an allowance recorded, Interest Income Recognized	0	0
Total, Recorded Investment	1,706		1,706		1,670
Total, Unpaid Principal Balance	1,763		1,763		1,675
Total, Related Allowance	5		5		0
Total, Average Recorded Investment	1,714	922	1,702	650
Total, Interest Income Recognized	1	0	1	1
SBA commercial business
Loans and Allowance for Loan Losses
Loans with no related allowance recorded, Recorded Investment	322		322		322
Loans with no related allowance recorded, Unpaid Principal Balance	416		416		416
Loans with no related allowance recorded, Related Allowance	0		0		0
Loans with no related allowance recorded, Average Recorded Investment	416	208	416	139
Loans with no related allowance recorded, Interest Income Recognized	0	0	0
Loans with an allowance recorded, Recorded Investment	446		446		373
Loans with an allowance recorded, Unpaid Principal Balance	553		553		399
Loans with an allowance recorded, Related Allowance	41		41		47
Loans with an allowance recorded, Average Recorded Investment	410	157	406	105
Loans with an allowance recorded, Interest Income Recognized	0	0
Total, Recorded Investment	768		768		695
Total, Unpaid Principal Balance	969		969		815
Total, Related Allowance	41		41		47
Total, Average Recorded Investment	826	365	822	244
Total, Interest Income Recognized	0	0
Consumer
Loans and Allowance for Loan Losses
Loans with no related allowance recorded, Recorded Investment	55		55		61
Loans with no related allowance recorded, Unpaid Principal Balance	56		56		63
Loans with no related allowance recorded, Related Allowance	0		0		0
Loans with no related allowance recorded, Average Recorded Investment	97	75	86	77
Loans with no related allowance recorded, Interest Income Recognized	0	0	1	2
Loans with an allowance recorded, Recorded Investment	107		107		138
Loans with an allowance recorded, Unpaid Principal Balance	107		107		138
Loans with an allowance recorded, Related Allowance	0		0		0
Loans with an allowance recorded, Average Recorded Investment	220	183	193	174
Loans with an allowance recorded, Interest Income Recognized	0	0
Total, Recorded Investment	162		162		199
Total, Unpaid Principal Balance	163		163		201
Total, Related Allowance	0		0		$ 0
Total, Average Recorded Investment	317	258	279	251
Total, Interest Income Recognized	$ 0	$ 0	$ 1	$ 2