Loans - Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	$ 4,303,992	$ 4,157,470
Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,449,174	1,497,272
Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	205,911	220,196
Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	76,488	49,274
Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	69,236	65,059
Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	351,635	334,529
Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	867,912	708,339
Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	173,534	177,244
Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,842,255	2,717,384
Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	476,012	438,245
Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	133,039	137,743
Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	62,536	60,806
Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	671,587	636,794
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	676,544	688,753
Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	111,872	113,627
Special Mention [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	159,081	209,932
Special Mention [Member] | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	79,747	101,936
Special Mention [Member] | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	13,211	28,137
Special Mention [Member] | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,859	2,531
Special Mention [Member] | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0	3,000
Special Mention [Member] | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	15,070	33,668
Special Mention [Member] | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	7,500	9,542
Special Mention [Member] | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	13,597	18,490
Special Mention [Member] | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	115,914	163,636
Special Mention [Member] | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	875	793
Special Mention [Member] | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	573	684
Special Mention [Member] | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0	0
Special Mention [Member] | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,448	1,477
Special Mention [Member] | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	33,318	42,223
Special Mention [Member] | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	8,401	2,596
Substandard [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	154,100	215,188
Substandard [Member] | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	86,426	135,282
Substandard [Member] | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	19,677	25,884
Substandard [Member] | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,649	2,427
Substandard [Member] | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	409	795
Substandard [Member] | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	21,735	29,106
Substandard [Member] | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	7,188	11,680
Substandard [Member] | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	10,245	6,737
Substandard [Member] | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	125,594	182,805
Substandard [Member] | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,524	1,764
Substandard [Member] | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	969	1,395
Substandard [Member] | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	392	415
Substandard [Member] | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,885	3,574
Substandard [Member] | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	23,833	27,184
Substandard [Member] | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,788	1,625
Doubtful [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	45,308	42,460
Doubtful [Member] | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	24,840	15,173
Doubtful [Member] | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	7,329	4,739
Doubtful [Member] | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	277	1,143
Doubtful [Member] | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	84	7,383
Doubtful [Member] | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	7,690	13,265
Doubtful [Member] | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	4,184	4,511
Doubtful [Member] | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,370	3,228
Doubtful [Member] | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	39,084	36,177
Doubtful [Member] | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	115	114
Doubtful [Member] | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	268	628
Doubtful [Member] | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,010	2,085
Doubtful [Member] | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,393	2,827
Doubtful [Member] | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	3,745	3,428
Doubtful [Member] | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	86	28
Total Criticized Loans [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	358,489	467,580
Total Criticized Loans [Member] | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	191,013	252,391
Total Criticized Loans [Member] | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	40,217	58,760
Total Criticized Loans [Member] | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	3,785	6,101
Total Criticized Loans [Member] | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	493	11,178
Total Criticized Loans [Member] | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	44,495	76,039
Total Criticized Loans [Member] | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	18,872	25,733
Total Criticized Loans [Member] | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	26,212	28,455
Total Criticized Loans [Member] | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	280,592	382,618
Total Criticized Loans [Member] | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,514	2,671
Total Criticized Loans [Member] | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,810	2,707
Total Criticized Loans [Member] | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,402	2,500
Total Criticized Loans [Member] | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	6,726	7,878
Total Criticized Loans [Member] | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	60,896	72,835
Total Criticized Loans [Member] | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	$ 10,275	$ 4,249