Schedule of Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 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					$ 387	$ 382
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 79,924	$ 75,336	$ 76,817	$ 74,200
Provision charged to operating expense	2,550	1,340	6,550	2,435
Less loans charged-off	(3,441)	(1,508)	(7,743)	(3,368)
Add back recoveries of loans previously charged-off	1,307	1,384	4,716	3,285
Ending balance	80,340	76,552	80,340	76,552
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					18,853	11,575
Loans collectively evaluated for impairment					61,487	65,242
Ending balance	79,924	75,336	76,817	74,200	80,340	76,817
Total loans:
Individually evaluated for impairment					98,484	91,965
Individually evaluated for impairment					5,241,705	5,101,356
Total loans					5,340,189	5,193,321
Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	36,652	53,659	52,296	53,884
Provision charged to operating expense	(4,059)	461	(20,140)	(570)
Less loans charged-off	(523)	(610)	(2,445)	(795)
Add back recoveries of loans previously charged-off	211	425	2,570	1,416
Ending balance	32,281	53,935	32,281	53,935
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					8,184	4,794
Loans collectively evaluated for impairment					24,097	47,502
Ending balance	36,652	53,659	52,296	53,884	32,281	52,296
Total loans:
Individually evaluated for impairment					64,204	66,516
Individually evaluated for impairment					3,400,311	3,346,546
Total loans					3,464,515	3,413,062
Total consumer loans
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	5,256	5,499	5,144	5,035
Provision charged to operating expense	2,123	646	3,352	1,771
Less loans charged-off	(1,712)	(837)	(3,604)	(2,138)
Add back recoveries of loans previously charged-off	648	520	1,423	1,160
Ending balance	6,315	5,828	6,315	5,828
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					0	0
Loans collectively evaluated for impairment					6,315	5,144
Ending balance	5,256	5,499	5,144	5,035	6,315	5,144
Total loans:
Individually evaluated for impairment					0	0
Individually evaluated for impairment					907,174	844,353
Total loans					907,174	844,353
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	36,252	15,196	18,775	14,307
Provision charged to operating expense	4,313	224	22,003	1,217
Less loans charged-off	(1,018)	(61)	(1,506)	(435)
Add back recoveries of loans previously charged-off	448	438	723	708
Ending balance	39,995	15,797	39,995	15,797
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					10,588	6,487
Loans collectively evaluated for impairment					29,407	12,288
Ending balance	36,252	15,196	18,775	14,307	39,995	18,775
Total loans:
Individually evaluated for impairment					33,506	24,471
Individually evaluated for impairment					791,456	767,945
Total loans					824,962	792,416
Agriculture
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,764	982	602	974
Provision charged to operating expense	173	9	1,335	17
Less loans charged-off	(188)	0	(188)	0
Add back recoveries of loans previously charged-off	0	1	0	1
Ending balance	1,749	992	1,749	992
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					81	294
Loans collectively evaluated for impairment					1,668	308
Ending balance	1,764	982	602	974	1,749	602
Total loans:
Individually evaluated for impairment					774	978
Individually evaluated for impairment					139,118	141,173
Total loans					139,892	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					3,646	1,339
Total loans					$ 3,646	$ 1,339