Loans - Schedule of Financing Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Sep. 30, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	$ 8,735,918	$ 7,351,288
Less:
Less: Unamortized discount on acquired loans	(39,947)	(19,264)
Unearned net deferred fees and costs and loans in process	(13,327)	(6,826)
Total	8,682,644	7,325,198
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	1,020,958	923,145
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	3,754,107	2,845,748
Commercial non real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	1,673,166	1,609,510
Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	2,168,937	1,861,465
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	76,273	73,049
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total financing receivables, gross	$ 42,477	$ 38,371