Loans and Allowance for Credit Losses (Details 1) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
Credit risk profile by creditworthiness
Loans	$ 4,159,531	$ 4,043,643	$ 3,992,058
Commercial, Financial, Agricultural and Other [Member]
Credit risk profile by creditworthiness
Loans	1,059,675	996,739
Real Estate Construction [Member]
Credit risk profile by creditworthiness
Loans	77,442	76,564
Residential Real Estate [Member]
Credit risk profile by creditworthiness
Loans	1,213,610	1,137,059
Commercial Real Estate [Member]
Credit risk profile by creditworthiness
Loans	1,232,270	1,267,432
Loans to Individuals [Member]
Credit risk profile by creditworthiness
Loans	576,534	565,849
Pass [Member]
Credit risk profile by creditworthiness
Loans	3,887,014	3,751,620
Pass [Member] | Commercial, Financial, Agricultural and Other [Member]
Credit risk profile by creditworthiness
Loans	955,231	904,057
Pass [Member] | Real Estate Construction [Member]
Credit risk profile by creditworthiness
Loans	50,028	44,914
Pass [Member] | Residential Real Estate [Member]
Credit risk profile by creditworthiness
Loans	1,202,163	1,126,143
Pass [Member] | Commercial Real Estate [Member]
Credit risk profile by creditworthiness
Loans	1,103,062	1,110,664
Pass [Member] | Loans to Individuals [Member]
Credit risk profile by creditworthiness
Loans	576,530	565,842
OAEM [Member]
Credit risk profile by creditworthiness
Loans	102,680	99,211
OAEM [Member] | Commercial, Financial, Agricultural and Other [Member]
Credit risk profile by creditworthiness
Loans	27,384	27,627
OAEM [Member] | Real Estate Construction [Member]
Credit risk profile by creditworthiness
Loans	699	4,238
OAEM [Member] | Residential Real Estate [Member]
Credit risk profile by creditworthiness
Loans	5,668	5,484
OAEM [Member] | Commercial Real Estate [Member]
Credit risk profile by creditworthiness
Loans	68,925	61,855
OAEM [Member] | Loans to Individuals [Member]
Credit risk profile by creditworthiness
Loans	4	7
Substandard [Member]
Credit risk profile by creditworthiness
Loans	164,126	182,160
Substandard [Member] | Commercial, Financial, Agricultural and Other [Member]
Credit risk profile by creditworthiness
Loans	77,060	60,114
Substandard [Member] | Real Estate Construction [Member]
Credit risk profile by creditworthiness
Loans	21,004	21,701
Substandard [Member] | Residential Real Estate [Member]
Credit risk profile by creditworthiness
Loans	5,779	5,432
Substandard [Member] | Commercial Real Estate [Member]
Credit risk profile by creditworthiness
Loans	60,283	94,913
Substandard [Member] | Loans to Individuals [Member]
Credit risk profile by creditworthiness
Loans	0	0
Doubtful [Member]
Credit risk profile by creditworthiness
Loans	5,711	10,652
Doubtful [Member] | Commercial, Financial, Agricultural and Other [Member]
Credit risk profile by creditworthiness
Loans	0	4,941
Doubtful [Member] | Real Estate Construction [Member]
Credit risk profile by creditworthiness
Loans	5,711	5,711
Doubtful [Member] | Residential Real Estate [Member]
Credit risk profile by creditworthiness
Loans	0	0
Doubtful [Member] | Commercial Real Estate [Member]
Credit risk profile by creditworthiness
Loans	0	0
Doubtful [Member] | Loans to Individuals [Member]
Credit risk profile by creditworthiness
Loans	0	0
Total Non-Pass [Member]
Credit risk profile by creditworthiness
Loans	272,517	292,023
Total Non-Pass [Member] | Commercial, Financial, Agricultural and Other [Member]
Credit risk profile by creditworthiness
Loans	104,444	92,682
Total Non-Pass [Member] | Real Estate Construction [Member]
Credit risk profile by creditworthiness
Loans	27,414	31,650
Total Non-Pass [Member] | Residential Real Estate [Member]
Credit risk profile by creditworthiness
Loans	11,447	10,916
Total Non-Pass [Member] | Commercial Real Estate [Member]
Credit risk profile by creditworthiness
Loans	129,208	156,768
Total Non-Pass [Member] | Loans to Individuals [Member]
Credit risk profile by creditworthiness
Loans	$ 4	$ 7