Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	$ 5,120,794	$ 4,856,615
Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,750,797	1,639,422
Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	212,990	220,443
Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	112,495	96,580
Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	93,775	101,246
Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	419,260	418,269
Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,020,445	999,903
Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	163,116	167,659
Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3,353,618	3,225,253
Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	616,142	552,863
Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	150,170	144,141
Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	65,649	65,467
Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	831,961	762,471
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	778,648	740,073
Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	154,855	124,859
Other Assets Especially Mentioned
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	155,157	154,084
Other Assets Especially Mentioned | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	76,483	84,533
Other Assets Especially Mentioned | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	14,928	11,826
Other Assets Especially Mentioned | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,230	2,029
Other Assets Especially Mentioned | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0	39
Other Assets Especially Mentioned | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	16,158	13,894
Other Assets Especially Mentioned | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	6,016	10,473
Other Assets Especially Mentioned | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	8,549	10,122
Other Assets Especially Mentioned | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	107,206	119,022
Other Assets Especially Mentioned | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	774	916
Other Assets Especially Mentioned | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	687	553
Other Assets Especially Mentioned | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0	0
Other Assets Especially Mentioned | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,461	1,469
Other Assets Especially Mentioned | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	43,384	25,766
Other Assets Especially Mentioned | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3,106	7,827
Substandard
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	163,846	163,675
Substandard | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	86,047	83,448
Substandard | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	16,137	15,016
Substandard | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2,219	2,666
Substandard | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	352	253
Substandard | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	18,708	17,935
Substandard | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	12,117	10,848
Substandard | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	16,095	12,328
Substandard | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	132,967	124,559
Substandard | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,180	1,590
Substandard | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	928	1,085
Substandard | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0	348
Substandard | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2,108	3,023
Substandard | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	21,213	32,433
Substandard | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	7,558	3,660
Doubtful
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	24,547	34,854
Doubtful | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	5,095	15,246
Doubtful | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	630	2,507
Doubtful | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	27	0
Doubtful | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	757	2,442
Doubtful | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,414	4,949
Doubtful | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	645	1,121
Doubtful | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	612	612
Doubtful | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	7,766	21,928
Doubtful | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	164	121
Doubtful | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	307	432
Doubtful | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0	1,263
Doubtful | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	471	1,816
Doubtful | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	15,638	10,273
Doubtful | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	672	837
Total Criticized Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	343,550	352,613
Total Criticized Loans | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	167,625	183,227
Total Criticized Loans | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	31,695	29,349
Total Criticized Loans | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3,476	4,695
Total Criticized Loans | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,109	2,734
Total Criticized Loans | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	36,280	36,778
Total Criticized Loans | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	18,778	22,442
Total Criticized Loans | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	25,256	23,062
Total Criticized Loans | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	247,939	265,509
Total Criticized Loans | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2,118	2,627
Total Criticized Loans | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,922	2,070
Total Criticized Loans | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0	1,611
Total Criticized Loans | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	4,040	6,308
Total Criticized Loans | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	80,235	68,472
Total Criticized Loans | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	$ 11,336	$ 12,324