Allowance for Loan and Lease Losses - Summary of Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	$ 64,642	$ 57,200
Charge-offs	(5,552)	(728)
Recoveries	628	767
Provision	6,950	4,086
Allowance for loan losses, ending balance	66,767	61,128
Acquired receivables subject to ASC 310-30
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	1,679
Recoveries	100	200
(Improvement) impairment of ASC 310-30 loans	99	(197)
Allowance for loan losses, ending balance	1,763
Residential real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	7,106	8,025
Charge-offs	(150)	(196)
Recoveries	205	44
Provision	(350)	22
Allowance for loan losses, ending balance	6,786	7,798
Residential real estate \| Acquired receivables subject to ASC 310-30
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	907
(Improvement) impairment of ASC 310-30 loans	(25)	(97)
Allowance for loan losses, ending balance	866
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	17,946	18,014
Charge-offs	0	(28)
Recoveries	99	83
Provision	(1,546)	1,366
Allowance for loan losses, ending balance	16,623	19,405
Commercial real estate \| Acquired receivables subject to ASC 310-30
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	772
(Improvement) impairment of ASC 310-30 loans	124	(30)
Allowance for loan losses, ending balance	897
Commercial non real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	12,990	15,996
Charge-offs	(1,959)	(45)
Recoveries	98	404
Provision	2,314	875
Allowance for loan losses, ending balance	13,443	17,160
Commercial non real estate \| Acquired receivables subject to ASC 310-30
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	0
(Improvement) impairment of ASC 310-30 loans	0	(70)
Allowance for loan losses, ending balance	0
Agriculture
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	25,115	13,952
Charge-offs	(2,866)	(11)
Recoveries	27	47
Provision	6,243	1,485
Allowance for loan losses, ending balance	28,519	15,473
Agriculture \| Acquired receivables subject to ASC 310-30
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	0
(Improvement) impairment of ASC 310-30 loans	0	0
Allowance for loan losses, ending balance	0
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	438	348
Charge-offs	(79)	(48)
Recoveries	15	25
Provision	(34)	16
Allowance for loan losses, ending balance	340	341
Consumer \| Acquired receivables subject to ASC 310-30
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	0
(Improvement) impairment of ASC 310-30 loans	0	0
Allowance for loan losses, ending balance	0
Other
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	1,047	865
Charge-offs	(498)	(400)
Recoveries	184	164
Provision	323	322
Allowance for loan losses, ending balance	1,056	951
Other \| Acquired receivables subject to ASC 310-30
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, beginning balance	0
(Improvement) impairment of ASC 310-30 loans	0	$ 0
Allowance for loan losses, ending balance	$ 0

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Amount, after recoveries, of loans and leases that have been written-off.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of expense related to estimated loss from loan and lease transactions.

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