Loans and Allowance for Credit Losses (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
Outstanding balances of loan
Loans	$ 4,159,531	$ 4,043,643	$ 3,992,058
Commercial, Financial, Agricultural and Other [Member]
Outstanding balances of loan
Loans	1,059,675	996,739
Real Estate Construction [Member]
Outstanding balances of loan
Loans	77,442	76,564
Residential Real Estate [Member]
Outstanding balances of loan
Loans	1,213,610	1,137,059
Commercial Real Estate [Member]
Outstanding balances of loan
Loans	1,232,270	1,267,432
Loans to Individuals [Member]
Outstanding balances of loan
Loans	$ 576,534	$ 565,849