Loans - Schedule of Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016
With an allowance recorded:
Recorded Investment	$ 148,149		$ 142,619
Unpaid Principal Balance	163,937		155,753
Related Allowance	26,266		25,686
With no allowance recorded:
Recorded Investment	72,168		73,810
Unpaid Principal Balance	79,383		78,855
Total Recorded Investment, Impaired Loans	220,317		216,429
Total Unpaid Principal Balance, Impaired Loans	243,320		234,608
Average recorded investment and interest income recognized on impaired loans:
Average Recorded Investment	218,374	$ 220,516
Interest Income Recognized while on Impaired Status	3,088	4,430
Residential real estate
With an allowance recorded:
Recorded Investment	5,941		6,244
Unpaid Principal Balance	6,595		6,886
Related Allowance	2,944		3,000
With no allowance recorded:
Recorded Investment	3,806		4,120
Unpaid Principal Balance	5,499		5,807
Average recorded investment and interest income recognized on impaired loans:
Average Recorded Investment	10,056	12,334
Interest Income Recognized while on Impaired Status	114	149
Commercial real estate
With an allowance recorded:
Recorded Investment	20,794		29,965
Unpaid Principal Balance	23,304		32,349
Related Allowance	2,471		3,846
With no allowance recorded:
Recorded Investment	29,245		24,040
Unpaid Principal Balance	31,187		24,660
Average recorded investment and interest income recognized on impaired loans:
Average Recorded Investment	52,022	74,411
Interest Income Recognized while on Impaired Status	670	1,469
Commercial non real estate
With an allowance recorded:
Recorded Investment	37,168		34,526
Unpaid Principal Balance	39,894		35,283
Related Allowance	7,220		6,475
With no allowance recorded:
Recorded Investment	10,407		15,299
Unpaid Principal Balance	11,935		16,469
Average recorded investment and interest income recognized on impaired loans:
Average Recorded Investment	48,700	56,171
Interest Income Recognized while on Impaired Status	422	356
Agriculture
With an allowance recorded:
Recorded Investment	83,901		71,501
Unpaid Principal Balance	93,789		80,842
Related Allowance	13,553		12,278
With no allowance recorded:
Recorded Investment	28,703		30,339
Unpaid Principal Balance	30,755		31,907
Average recorded investment and interest income recognized on impaired loans:
Average Recorded Investment	107,222	77,324
Interest Income Recognized while on Impaired Status	1,867	2,439
Consumer
With an allowance recorded:
Recorded Investment	345		383
Unpaid Principal Balance	355		393
Related Allowance	78		87
With no allowance recorded:
Recorded Investment	7		12
Unpaid Principal Balance	7		$ 12
Average recorded investment and interest income recognized on impaired loans:
Average Recorded Investment	374	276
Interest Income Recognized while on Impaired Status	$ 15	$ 17