Schedule of Loans by Class (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Loans and Leases Receivable [Line Items]
Loans held for investment	$ 4,223,078	$ 4,157,470
Mortgage loans held for sale	74,286	66,442
Total loans	4,297,364	4,223,912	4,169,963
Commercial real estate
Loans and Leases Receivable [Line Items]
Loans held for investment	1,447,145	1,497,272
Land acquisition & development construction real estate
Loans and Leases Receivable [Line Items]
Loans held for investment	210,761	220,196
Residential construction real estate
Loans and Leases Receivable [Line Items]
Loans held for investment	60,883	49,274
Commercial construction real estate
Loans and Leases Receivable [Line Items]
Loans held for investment	65,567	65,059
Total construction loans
Loans and Leases Receivable [Line Items]
Loans held for investment	337,211	334,529
Residential real estate
Loans and Leases Receivable [Line Items]
Loans held for investment	804,200	708,339
Agricultural real estate
Loans and Leases Receivable [Line Items]
Loans held for investment	176,799	177,244
Total real estate loans
Loans and Leases Receivable [Line Items]
Loans held for investment	2,765,355	2,717,384
Indirect consumer
Loans and Leases Receivable [Line Items]
Loans held for investment	457,151	438,245
Other consumer
Loans and Leases Receivable [Line Items]
Loans held for investment	136,459	137,743
Credit card consumer
Loans and Leases Receivable [Line Items]
Loans held for investment	59,334	60,806
Total consumer loans
Loans and Leases Receivable [Line Items]
Loans held for investment	652,944	636,794
Commercial
Loans and Leases Receivable [Line Items]
Loans held for investment	680,751	688,753
Agricultural
Loans and Leases Receivable [Line Items]
Loans held for investment	121,530	113,627
Other, including overdrafts
Loans and Leases Receivable [Line Items]
Loans held for investment	$ 2,498	$ 912