Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	$ 54,051	$ 51,756	$ 54,324	$ 48,685
Charge-offs	(5,759)	(3,283)	(12,243)	(7,839)
Recoveries	888	852	2,569	4,294
Provision	5,705	5,328	10,235	9,513
Ending Balance	54,885	54,653	54,885	54,653
Agricultural and agricultural real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	3,832	4,100	4,210	3,887
Charge-offs	0	0	(888)	0
Recoveries	14	2	17	9
Provision	2,281	904	2,788	1,110
Ending Balance	6,127	5,006	6,127	5,006
Residential real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	2,263	2,065	2,263	1,934
Charge-offs	(142)	(106)	(541)	(248)
Recoveries	63	1	70	25
Provision	82	22	474	271
Ending Balance	2,266	1,982	2,266	1,982
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	8,927	7,098	8,767	7,237
Charge-offs	(1,750)	(2,123)	(4,982)	(4,775)
Recoveries	418	263	987	766
Provision	1,387	1,855	4,210	3,865
Ending Balance	8,982	7,093	8,982	7,093
Commercial | Commercial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	17,168	15,525	14,765	16,095
Charge-offs	(1,954)	(240)	(3,310)	(587)
Recoveries	347	119	635	438
Provision	1,409	1,487	4,880	945
Ending Balance	16,970	16,891	16,970	16,891
Commercial real estate | Commercial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	21,861	22,968	24,319	19,532
Charge-offs	(1,913)	(814)	(2,522)	(2,229)
Recoveries	46	467	860	3,056
Provision	546	1,060	(2,117)	3,322
Ending Balance	$ 20,540	$ 23,681	$ 20,540	$ 23,681