Loans and Allowance for Loan Losses - Mortgage Servicing Rights (Details) - Mortgage Servicing Rights [Member]	6 Months Ended	12 Months Ended
Mar. 31, 2021	Sep. 30, 2020
Discount rate	9.00%	9.25%
Maximum [Member]
Prepayment rate	79.65%	86.98%
Minimum [Member]
Prepayment rate	2.78%	2.99%
Weighted Average [Member]
Prepayment rate	10.09%	18.08%

Discount rate used to estimate the fair value of servicing assets and servicing liabilities.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122596-111746

Name:	us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration