Loans - Schedule of Loans by Class (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Loans and Leases Receivable
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
Commercial real estate
Loans and Leases Receivable
Loans held for investment	1,497,272	1,553,155
Land acquisition & development construction real estate
Loans and Leases Receivable
Loans held for investment	220,196	278,613
Residential construction real estate
Loans and Leases Receivable
Loans held for investment	49,274	61,106
Commercial construction real estate
Loans and Leases Receivable
Loans held for investment	65,059	61,054
Total construction loans
Loans and Leases Receivable
Loans held for investment	334,529	400,773
Residential real estate
Loans and Leases Receivable
Loans held for investment	708,339	571,943
Loans receivable, maturity	15 years
Agricultural real estate
Loans and Leases Receivable
Loans held for investment	177,244	175,302
Total real estate loans
Loans and Leases Receivable
Loans held for investment	2,717,384	2,701,173
Indirect consumer
Loans and Leases Receivable
Loans held for investment	438,245	407,651
Other consumer
Loans and Leases Receivable
Loans held for investment	137,743	147,487
Credit card consumer
Loans and Leases Receivable
Loans held for investment	60,806	60,933
Total consumer loans
Loans and Leases Receivable
Loans held for investment	636,794	616,071
Commercial
Loans and Leases Receivable
Loans held for investment	688,753	693,261
Agricultural
Loans and Leases Receivable
Loans held for investment	113,627	119,710
Other, including overdrafts
Loans and Leases Receivable
Loans held for investment	912	2,813
Home equity line of credit
Loans and Leases Receivable
Loans held for investment	$ 273,739	$ 312,295
Loans receivable, loan to value limit	80.00%
Commercial and agricultural real estate
Loans and Leases Receivable
Loans receivable, maturity	5 years