Schedule of Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses				$ 382	$ 427
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 76,817	$ 74,200	$ 85,339
Provision charged to operating expense	9,991	6,822	(6,622)
Less loans charged-off	(19,843)	(11,637)	(13,995)
Add back recoveries of loans previously charged-off	9,249	7,432	9,478
Ending balance	76,214	76,817	74,200
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment				13,954	11,575	$ 5,792
Loans collectively evaluated for impairment				62,260	65,242	68,408
Ending balance	76,817	74,200	85,339	76,214	76,817	74,200
Total loans:
Individually evaluated for impairment				104,691	91,965	78,480
Individually evaluated for impairment				5,312,059	5,101,356	4,778,135
Total Loans				5,416,750	5,193,321	4,856,615
Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	52,296	53,884	63,923
Provision charged to operating expense	(21,714)	(645)	(10,348)
Less loans charged-off	(5,215)	(4,076)	(3,014)
Add back recoveries of loans previously charged-off	3,258	3,133	3,323
Ending balance	28,625	52,296	53,884
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment				4,588	4,794	3,961
Loans collectively evaluated for impairment				24,037	47,502	49,923
Ending balance	52,296	53,884	63,923	28,625	52,296	53,884
Total loans:
Individually evaluated for impairment				68,632	66,516	62,775
Individually evaluated for impairment				3,445,451	3,346,546	3,162,478
Total Loans				3,514,083	3,413,062	3,225,253
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	5,144	5,035	6,193
Provision charged to operating expense	8,393	3,243	1,382
Less loans charged-off	(8,607)	(5,683)	(4,887)
Add back recoveries of loans previously charged-off	2,781	2,549	2,347
Ending balance	7,711	5,144	5,035
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment				0	0	0
Loans collectively evaluated for impairment				7,711	5,144	5,035
Ending balance	5,144	5,035	6,193	7,711	5,144	5,035
Total loans:
Individually evaluated for impairment				0	0	0
Individually evaluated for impairment				970,266	844,353	762,471
Total Loans				970,266	844,353	762,471
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	18,775	14,307	14,747
Provision charged to operating expense	21,950	4,376	1,809
Less loans charged-off	(5,838)	(1,657)	(6,030)
Add back recoveries of loans previously charged-off	3,205	1,749	3,781
Ending balance	38,092	18,775	14,307
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment				9,254	6,487	1,190
Loans collectively evaluated for impairment				28,838	12,288	13,117
Ending balance	18,775	14,307	14,747	38,092	18,775	14,307
Total loans:
Individually evaluated for impairment				32,397	24,471	14,526
Individually evaluated for impairment				765,545	767,945	725,547
Total Loans				797,942	792,416	740,073
Agriculture
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	602	974	476
Provision charged to operating expense	1,362	(152)	535
Less loans charged-off	(183)	(221)	(64)
Add back recoveries of loans previously charged-off	5	1	27
Ending balance	1,786	602	974
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment				112	294	641
Loans collectively evaluated for impairment				1,674	308	333
Ending balance	602	974	476	1,786	602	974
Total loans:
Individually evaluated for impairment				3,662	978	1,179
Individually evaluated for impairment				129,196	141,173	123,680
Total Loans				132,858	142,151	124,859
Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0	0
Provision charged to operating expense	0	0	0
Less loans charged-off	0	0	0
Add back recoveries of loans previously charged-off	0	0	0
Ending balance	0	0	0
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment				0	0	0
Loans collectively evaluated for impairment				0	0	0
Ending balance	$ 0	$ 0	$ 0	0	0	0
Total loans:
Individually evaluated for impairment				0	0	0
Individually evaluated for impairment				1,601	1,339	3,959
Total Loans				$ 1,601	$ 1,339	$ 3,959