Loans and Allowance for Credit Losses Credit Quality Indicators (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	$ 11,940,005	$ 11,975,964
Commercial Loans, Commercial Mortgages, Constructions Loans [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	8,671,841	8,804,282
Percentage of total loans rated	100.00%	100.00%
Real-estate commercial mortage [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	4,632,509	4,602,596
Commercial - industrial, financial, and agricultural
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	3,507,846	3,639,368
Commercial - Secured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	3,296,019	3,393,559
Commercial - Unsecured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	211,827	245,809
Construction, Excluding Contstruction Other [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	531,486	562,318
Construction - Commercial Residential [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	312,657	352,938
Construction - Commercial [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	218,829	209,380
Pass [Member] | Commercial Loans, Commercial Mortgages, Constructions Loans [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	7,693,318	7,669,777
Percentage of total loans rated	88.70%	87.10%
Pass [Member] | Real-estate commercial mortage [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	4,199,788	4,099,103
Pass [Member] | Commercial - industrial, financial, and agricultural
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	3,126,304	3,208,919
Pass [Member] | Commercial - Secured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	2,926,402	2,977,957
Pass [Member] | Commercial - Unsecured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	199,902	230,962
Pass [Member] | Construction, Excluding Contstruction Other [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	367,226	361,755
Pass [Member] | Construction - Commercial Residential [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	164,247	175,706
Pass [Member] | Construction - Commercial [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	202,979	186,049
Special Mention [Member] | Commercial Loans, Commercial Mortgages, Constructions Loans [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	346,255	391,465
Percentage of total loans rated	4.00%	4.50%
Special Mention [Member] | Real-estate commercial mortage [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	130,340	160,935
Special Mention [Member] | Commercial - industrial, financial, and agricultural
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	161,034	172,654
Special Mention [Member] | Commercial - Secured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	154,759	166,588
Special Mention [Member] | Commercial - Unsecured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	6,275	6,066
Special Mention [Member] | Construction, Excluding Contstruction Other [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	54,881	57,876
Special Mention [Member] | Construction - Commercial Residential [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	51,452	50,854
Special Mention [Member] | Construction - Commercial [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	3,429	7,022
Substandard [Member] | Commercial Loans, Commercial Mortgages, Constructions Loans [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	632,268	743,040
Percentage of total loans rated	7.30%	8.40%
Substandard [Member] | Real-estate commercial mortage [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	302,381	342,558
Substandard [Member] | Commercial - industrial, financial, and agricultural
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	220,508	257,795
Substandard [Member] | Commercial - Secured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	214,858	249,014
Substandard [Member] | Commercial - Unsecured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	5,650	8,781
Substandard [Member] | Construction, Excluding Contstruction Other [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	109,379	142,687
Substandard [Member] | Construction - Commercial Residential [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	96,958	126,378
Substandard [Member] | Construction - Commercial [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	$ 12,421	$ 16,309