Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	$ 4,326,367	$ 4,303,992
Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,452,967	1,449,174
Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	197,582	205,911
Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	81,411	76,488
Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	75,356	69,236
Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	354,349	351,635
Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	868,836	867,912
Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	160,570	173,534
Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2,836,722	2,842,255
Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	481,482	476,012
Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	130,614	133,039
Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	58,310	62,536
Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	670,406	671,587
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	707,237	676,544
Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	108,376	111,872
Other Assets Especially Mentioned
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	174,834	159,081
Other Assets Especially Mentioned | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	85,017	79,747
Other Assets Especially Mentioned | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	12,249	13,211
Other Assets Especially Mentioned | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2,386	1,859
Other Assets Especially Mentioned | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	272	0
Other Assets Especially Mentioned | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	14,907	15,070
Other Assets Especially Mentioned | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	10,586	7,500
Other Assets Especially Mentioned | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	13,717	13,597
Other Assets Especially Mentioned | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	124,227	115,914
Other Assets Especially Mentioned | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	949	875
Other Assets Especially Mentioned | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	504	573
Other Assets Especially Mentioned | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment		0
Other Assets Especially Mentioned | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,453	1,448
Other Assets Especially Mentioned | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	37,291	33,318
Other Assets Especially Mentioned | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	11,863	8,401
Substandard
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	161,103	154,100
Substandard | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	83,404	86,426
Substandard | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	19,994	19,677
Substandard | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,594	1,649
Substandard | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	461	409
Substandard | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	22,049	21,735
Substandard | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	10,498	7,188
Substandard | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	10,865	10,245
Substandard | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	126,816	125,594
Substandard | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,654	1,524
Substandard | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	804	969
Substandard | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	239	392
Substandard | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2,697	2,885
Substandard | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	29,513	23,833
Substandard | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2,077	1,788
Doubtful
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	31,672	45,308
Doubtful | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	18,834	24,840
Doubtful | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2,966	7,329
Doubtful | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0	277
Doubtful | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	82	84
Doubtful | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3,048	7,690
Doubtful | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,137	4,184
Doubtful | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2,316	2,370
Doubtful | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	25,335	39,084
Doubtful | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	112	115
Doubtful | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	377	268
Doubtful | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,671	2,010
Doubtful | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2,160	2,393
Doubtful | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3,853	3,745
Doubtful | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	324	86
Total Criticized Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	367,609	358,489
Total Criticized Loans | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	187,255	191,013
Total Criticized Loans | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	35,209	40,217
Total Criticized Loans | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3,980	3,785
Total Criticized Loans | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	815	493
Total Criticized Loans | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	40,004	44,495
Total Criticized Loans | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	22,221	18,872
Total Criticized Loans | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	26,898	26,212
Total Criticized Loans | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	276,378	280,592
Total Criticized Loans | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2,715	2,514
Total Criticized Loans | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,685	1,810
Total Criticized Loans | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,910	2,402
Total Criticized Loans | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	6,310	6,726
Total Criticized Loans | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	70,657	60,896
Total Criticized Loans | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	$ 14,264	$ 10,275