Loans - Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	$ 4,157,470	$ 4,133,028
Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,497,272	1,553,155
Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	220,196	278,613
Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	49,274	61,106
Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	65,059	61,054
Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	334,529	400,773
Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	708,339	571,943
Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	177,244	175,302
Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,717,384	2,701,173
Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	438,245	407,651
Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	137,743	147,487
Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	60,806	60,933
Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	636,794	616,071
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	688,753	693,261
Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	113,627	119,710
Other Assets Especially Mentioned
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	209,932	240,903
Other Assets Especially Mentioned | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	101,936	129,046
Other Assets Especially Mentioned | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	28,137	37,294
Other Assets Especially Mentioned | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,531	9,448
Other Assets Especially Mentioned | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	3,000	0
Other Assets Especially Mentioned | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	33,668	46,742
Other Assets Especially Mentioned | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	9,542	8,149
Other Assets Especially Mentioned | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	18,490	16,037
Other Assets Especially Mentioned | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	163,636	199,974
Other Assets Especially Mentioned | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	793	1,141
Other Assets Especially Mentioned | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	684	745
Other Assets Especially Mentioned | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0	0
Other Assets Especially Mentioned | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,477	1,886
Other Assets Especially Mentioned | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	42,223	34,698
Other Assets Especially Mentioned | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,596	4,345
Substandard
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	215,188	269,794
Substandard | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	135,282	153,320
Substandard | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	25,884	31,873
Substandard | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,427	5,528
Substandard | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	795	2,620
Substandard | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	29,106	40,021
Substandard | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	11,680	15,706
Substandard | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	6,737	18,498
Substandard | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	182,805	227,545
Substandard | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,764	1,729
Substandard | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,395	1,361
Substandard | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	415	486
Substandard | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	3,574	3,576
Substandard | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	27,184	33,478
Substandard | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,625	5,195
Doubtful
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	42,460	120,165
Doubtful | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	15,173	25,087
Doubtful | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	4,739	38,761
Doubtful | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,143	2,044
Doubtful | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	7,383	21,916
Doubtful | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	13,265	62,721
Doubtful | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	4,511	15,140
Doubtful | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	3,228	395
Doubtful | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	36,177	103,343
Doubtful | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	114	247
Doubtful | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	628	674
Doubtful | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,085	2,789
Doubtful | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,827	3,710
Doubtful | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	3,428	12,849
Doubtful | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	28	263
Total Criticized Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	467,580	630,862
Total Criticized Loans | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	252,391	307,453
Total Criticized Loans | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	58,760	107,928
Total Criticized Loans | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	6,101	17,020
Total Criticized Loans | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	11,178	24,536
Total Criticized Loans | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	76,039	149,484
Total Criticized Loans | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	25,733	38,995
Total Criticized Loans | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	28,455	34,930
Total Criticized Loans | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	382,618	530,862
Total Criticized Loans | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,671	3,117
Total Criticized Loans | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,707	2,780
Total Criticized Loans | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,500	3,275
Total Criticized Loans | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	7,878	9,172
Total Criticized Loans | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	72,835	81,025
Total Criticized Loans | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	$ 4,249	$ 9,803