Loans - Schedule of Financing Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	$ 10,111,602	$ 9,732,684
Less:
Less: Unamortized discount on acquired loans	(8,215)	(13,655)
Unearned net deferred fees and costs and net loans in process	(27,245)	(12,266)
Total	10,076,142	9,706,763
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	5,274,941	5,092,410
Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	1,724,350	2,008,644
Commercial non-real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	2,181,656	1,719,956
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	830,102	812,208
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	63,206	51,925
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	$ 37,347	$ 47,541