Schedule of Loans by Class (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Loans and Leases Receivable [Line Items]
Loans held for investment	$ 4,169,116	$ 4,157,470
Mortgage loans held for sale	55,443	66,442
Total loans	4,224,559	4,223,912	4,158,616
Commercial real estate
Loans and Leases Receivable [Line Items]
Loans held for investment	1,469,302	1,497,272
Land acquisition & development construction real estate
Loans and Leases Receivable [Line Items]
Loans held for investment	215,505	220,196
Residential construction real estate
Loans and Leases Receivable [Line Items]
Loans held for investment	50,153	49,274
Commercial construction real estate
Loans and Leases Receivable [Line Items]
Loans held for investment	65,228	65,059
Total construction loans
Loans and Leases Receivable [Line Items]
Loans held for investment	330,886	334,529
Residential real estate
Loans and Leases Receivable [Line Items]
Loans held for investment	758,480	708,339
Agricultural real estate
Loans and Leases Receivable [Line Items]
Loans held for investment	172,522	177,244
Total real estate loans
Loans and Leases Receivable [Line Items]
Loans held for investment	2,731,190	2,717,384
Indirect consumer
Loans and Leases Receivable [Line Items]
Loans held for investment	444,257	438,245
Other consumer
Loans and Leases Receivable [Line Items]
Loans held for investment	135,474	137,743
Credit card consumer
Loans and Leases Receivable [Line Items]
Loans held for investment	56,633	60,806
Total consumer loans
Loans and Leases Receivable [Line Items]
Loans held for investment	636,364	636,794
Commercial
Loans and Leases Receivable [Line Items]
Loans held for investment	688,844	688,753
Agricultural
Loans and Leases Receivable [Line Items]
Loans held for investment	111,411	113,627
Other, including overdrafts
Loans and Leases Receivable [Line Items]
Loans held for investment	$ 1,307	$ 912