Loans - Subsequent Defaults on Modified Loans (Details) $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2020 USD ($) contract	Mar. 31, 2019 USD ($) contract	Mar. 31, 2020 USD ($) contract	Mar. 31, 2019 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| contract	17	0	20	0
Recorded Investment \| $	$ 2,106	$ 0	$ 14,014	$ 0
Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| contract	0	0	0	0
Recorded Investment \| $	$ 0	$ 0	$ 0	$ 0
Agriculture
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| contract	17	0	19	0
Recorded Investment \| $	$ 2,106	$ 0	$ 11,180	$ 0
Commercial non-real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| contract	0	0	1	0
Recorded Investment \| $	$ 0	$ 0	$ 2,834	$ 0
Residential real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| contract	0	0	0	0
Recorded Investment \| $	$ 0	$ 0	$ 0	$ 0
Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| contract	0	0	0	0
Recorded Investment \| $	$ 0	$ 0	$ 0	$ 0

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Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953682-111524

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- Definition

Amount of financing receivable modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953682-111524

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