Loans - Schedule of Recorded Investment in Past Due Loans by Class (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Loans and Leases Receivable Recorded Investment, Past Due
Loans held for investment	$ 4,157,470	$ 4,133,028
Mortgage loans held for sale	66,442	53,521
Total loans	4,223,912	4,186,549
Interest Income on Non-Accrual Loans if Accrued	8,537	12,508	8,942
Commercial real estate
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	5,449	22,124
60 to 89 Days Past Due	3,163	7,871
Greater than 90 Days Past Due	2	630
Total Loans 30 or More Days Past Due	8,614	30,625
Current Loans	1,438,142	1,455,139
Non-accrual Loans	50,516	67,391
Loans held for investment	1,497,272	1,553,155
Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	3,371	5,251
60 to 89 Days Past Due	2,121	2,448
Greater than 90 Days Past Due	318	867
Total Loans 30 or More Days Past Due	5,810	8,566
Current Loans	195,077	208,134
Non-accrual Loans	19,309	61,913
Loans held for investment	220,196	278,613
Residential construction real estate
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	283	415
60 to 89 Days Past Due	0	0
Greater than 90 Days Past Due	0	0
Total Loans 30 or More Days Past Due	283	415
Current Loans	46,816	56,219
Non-accrual Loans	2,175	4,472
Loans held for investment	49,274	61,106
Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	0	1,698
60 to 89 Days Past Due	0	0
Greater than 90 Days Past Due	0	0
Total Loans 30 or More Days Past Due	0	1,698
Current Loans	56,933	34,820
Non-accrual Loans	8,126	24,536
Loans held for investment	65,059	61,054
Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	3,654	7,364
60 to 89 Days Past Due	2,121	2,448
Greater than 90 Days Past Due	318	867
Total Loans 30 or More Days Past Due	6,093	10,679
Current Loans	298,826	299,173
Non-accrual Loans	29,610	90,921
Loans held for investment	334,529	400,773
Residential real estate
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	3,896	4,669
60 to 89 Days Past Due	969	973
Greater than 90 Days Past Due	1,085	1,798
Total Loans 30 or More Days Past Due	5,950	7,440
Current Loans	691,963	546,278
Non-accrual Loans	10,426	18,225
Loans held for investment	708,339	571,943
Agricultural real estate
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	1,187	4,103
60 to 89 Days Past Due	0	1,831
Greater than 90 Days Past Due	218	0
Total Loans 30 or More Days Past Due	1,405	5,934
Current Loans	171,009	166,119
Non-accrual Loans	4,830	3,249
Loans held for investment	177,244	175,302
Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	14,186	38,260
60 to 89 Days Past Due	6,253	13,123
Greater than 90 Days Past Due	1,623	3,295
Total Loans 30 or More Days Past Due	22,062	54,678
Current Loans	2,599,940	2,466,709
Non-accrual Loans	95,382	179,786
Loans held for investment	2,717,384	2,701,173
Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	3,218	3,078
60 to 89 Days Past Due	512	370
Greater than 90 Days Past Due	32	45
Total Loans 30 or More Days Past Due	3,762	3,493
Current Loans	434,200	403,695
Non-accrual Loans	283	463
Loans held for investment	438,245	407,651
Other consumer
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	1,044	1,479
60 to 89 Days Past Due	104	436
Greater than 90 Days Past Due	31	60
Total Loans 30 or More Days Past Due	1,179	1,975
Current Loans	135,574	144,625
Non-accrual Loans	990	887
Loans held for investment	137,743	147,487
Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	409	604
60 to 89 Days Past Due	278	375
Greater than 90 Days Past Due	392	585
Total Loans 30 or More Days Past Due	1,079	1,564
Current Loans	59,704	59,343
Non-accrual Loans	23	26
Loans held for investment	60,806	60,933
Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	4,671	5,161
60 to 89 Days Past Due	894	1,181
Greater than 90 Days Past Due	455	690
Total Loans 30 or More Days Past Due	6,020	7,032
Current Loans	629,478	607,663
Non-accrual Loans	1,296	1,376
Loans held for investment	636,794	616,071
Commercial
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	5,463	13,721
60 to 89 Days Past Due	1,064	3,464
Greater than 90 Days Past Due	216	405
Total Loans 30 or More Days Past Due	6,743	17,590
Current Loans	671,414	657,609
Non-accrual Loans	10,596	18,062
Loans held for investment	688,753	693,261
Agricultural
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	1,710	476
60 to 89 Days Past Due	361	215
Greater than 90 Days Past Due	0	110
Total Loans 30 or More Days Past Due	2,071	801
Current Loans	111,031	118,150
Non-accrual Loans	525	759
Loans held for investment	113,627	119,710
Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	0	0
60 to 89 Days Past Due	0	2
Greater than 90 Days Past Due	0	0
Total Loans 30 or More Days Past Due	0	2
Current Loans	912	2,811
Non-accrual Loans	0	0
Loans held for investment	912	2,813
Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	26,030	57,618
60 to 89 Days Past Due	8,572	17,985
Greater than 90 Days Past Due	2,294	4,500
Total Loans 30 or More Days Past Due	36,896	80,103
Current Loans	4,012,775	3,852,942
Non-accrual Loans	107,799	199,983
Loans held for investment	4,157,470	4,133,028
Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	0	0
60 to 89 Days Past Due	0	0
Greater than 90 Days Past Due	0	0
Total Loans 30 or More Days Past Due	0	0
Current Loans	66,442	53,521
Non-accrual Loans	0	0
Total loans
Loans and Leases Receivable Recorded Investment, Past Due
30 to 59 Days Past Due	26,030	57,618
60 to 89 Days Past Due	8,572	17,985
Greater than 90 Days Past Due	2,294	4,500
Total Loans 30 or More Days Past Due	36,896	80,103
Current Loans	4,079,217	3,906,463
Non-accrual Loans	107,799	199,983
Total loans	$ 4,223,912	$ 4,186,549