Schedule of Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Certain Loans and Debt Securities Acquired in Transfer, Allowance for Credit Losses Due to Subsequent Impairment					$ 433	$ 382
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 80,340	$ 76,552	$ 76,817	$ 74,200
Provision charged to operating expense	2,363	1,098	8,913	3,533
Less loans charged-off	(3,115)	(4,547)	(10,858)	(7,916)
Add back recoveries of loans previously charged-off	1,647	1,153	6,363	4,439
Ending balance	81,235	74,256	81,235	74,256
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					18,565	11,575
Loans collectively evaluated for impairment					62,670	65,242
Ending balance	80,340	76,552	76,817	74,200	81,235	76,817
Total loans:
Individually evaluated for impairment					99,142	91,965
Individually evaluated for impairment					5,363,794	5,101,356
Total loans					5,462,936	5,193,321
Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	32,281	53,935	52,296	53,884
Provision charged to operating expense	(352)	(1,149)	(20,492)	(1,718)
Less loans charged-off	(379)	(2,219)	(2,824)	(3,014)
Add back recoveries of loans previously charged-off	221	389	2,791	1,804
Ending balance	31,771	50,956	31,771	50,956
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					7,576	4,794
Loans collectively evaluated for impairment					24,195	47,502
Ending balance	32,281	53,935	52,296	53,884	31,771	52,296
Total loans:
Individually evaluated for impairment					61,218	66,516
Individually evaluated for impairment					3,479,849	3,346,546
Total loans					3,541,067	3,413,062
Total consumer loans
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	6,315	5,828	5,144	5,035
Provision charged to operating expense	2,395	430	5,747	2,201
Less loans charged-off	(2,157)	(1,537)	(5,761)	(3,675)
Add back recoveries of loans previously charged-off	742	653	2,165	1,813
Ending balance	7,295	5,374	7,295	5,374
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					0	0
Loans collectively evaluated for impairment					7,295	5,144
Ending balance	6,315	5,828	5,144	5,035	7,295	5,144
Total loans:
Individually evaluated for impairment					0	0
Individually evaluated for impairment					952,385	844,353
Total loans					952,385	844,353
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	39,995	15,797	18,775	14,307
Provision charged to operating expense	265	2,004	22,268	3,220
Less loans charged-off	(579)	(791)	(2,085)	(1,227)
Add back recoveries of loans previously charged-off	680	111	1,403	821
Ending balance	40,361	17,121	40,361	17,121
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					10,912	6,487
Loans collectively evaluated for impairment					29,449	12,288
Ending balance	39,995	15,797	18,775	14,307	40,361	18,775
Total loans:
Individually evaluated for impairment					34,189	24,471
Individually evaluated for impairment					780,203	767,945
Total loans					814,392	792,416
Agriculture
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,749	992	602	974
Provision charged to operating expense	55	(187)	1,390	(170)
Less loans charged-off	0	0	(188)	0
Add back recoveries of loans previously charged-off	4	0	4	1
Ending balance	1,808	805	1,808	805
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					77	294
Loans collectively evaluated for impairment					1,731	308
Ending balance	1,749	992	602	974	1,808	602
Total loans:
Individually evaluated for impairment					3,735	978
Individually evaluated for impairment					149,065	141,173
Total loans					152,800	142,151
Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0	0	0
Provision charged to operating expense	0	0	0	0
Less loans charged-off	0	0	0	0
Add back recoveries of loans previously charged-off	0	0	0	0
Ending balance	0	0	0	0
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					0	0
Loans collectively evaluated for impairment					0	0
Ending balance	$ 0	$ 0	$ 0	$ 0	0	0
Total loans:
Individually evaluated for impairment					0	0
Individually evaluated for impairment					2,292	1,339
Total loans					$ 2,292	$ 1,339