The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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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.

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Allowance for Loan and Lease Losses - Summary of Allowance for Loan Losses by Type (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 20,037	$ 22,535
Collectively evaluated for impairment	43,297	39,975
Total allowance	64,540	63,503	$ 64,642	$ 57,200
Financing Receivables
Individually evaluated for impairment	208,054	207,923
Collectively evaluated for impairment	8,117,415	7,486,498
Loans Outstanding	8,396,314	7,787,016
Receivables acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	1,206	993
Financing Receivables
Loans Outstanding	70,845	92,595
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,668	3,621
Collectively evaluated for impairment	12,430	12,638
Total allowance	16,777	16,941	17,946	18,014
Financing Receivables
Individually evaluated for impairment	40,900	37,471
Collectively evaluated for impairment	4,053,712	3,487,232
Loans Outstanding	4,121,613	3,554,802
Commercial real estate \| Receivables acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	679	682
Financing Receivables
Loans Outstanding	27,001	30,099
Agriculture
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	9,590	11,468
Collectively evaluated for impairment	18,266	14,174
Total allowance	28,121	25,757	25,115	13,952
Financing Receivables
Individually evaluated for impairment	137,225	130,475
Collectively evaluated for impairment	1,823,947	1,702,634
Loans Outstanding	1,963,987	1,840,283
Agriculture \| Receivables acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	265	115
Financing Receivables
Loans Outstanding	2,815	7,174
Commercial non-real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	4,508	4,779
Collectively evaluated for impairment	9,102	9,335
Total allowance	13,610	14,114	12,990	15,996
Financing Receivables
Individually evaluated for impairment	23,082	31,933
Collectively evaluated for impairment	1,364,511	1,333,888
Loans Outstanding	1,388,009	1,367,741
Commercial non-real estate \| Receivables acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	0	0
Financing Receivables
Loans Outstanding	416	1,920
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	2,210	2,581
Collectively evaluated for impairment	2,277	2,570
Total allowance	4,749	5,347	7,106	8,025
Financing Receivables
Individually evaluated for impairment	6,686	7,751
Collectively evaluated for impairment	780,047	854,330
Loans Outstanding	826,758	914,817
Residential real estate \| Receivables acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	262	196
Financing Receivables
Loans Outstanding	40,025	52,736
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	61	86
Collectively evaluated for impairment	196	243
Total allowance	257	329	438	348
Financing Receivables
Individually evaluated for impairment	161	293
Collectively evaluated for impairment	48,711	65,207
Loans Outstanding	49,460	66,166
Consumer \| Receivables acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	0	0
Financing Receivables
Loans Outstanding	588	666
Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	1,026	1,015
Total allowance	1,026	1,015	$ 1,047	$ 865
Financing Receivables
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	46,487	43,207
Loans Outstanding	46,487	43,207
Other \| Receivables acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance	0	0
Financing Receivables
Loans Outstanding	$ 0	$ 0