Loans and Allowance for Credit Losses Credit Quality Indicators (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	$ 12,653,095	$ 12,154,209
Commercial Loans, Commercial Mortgages, Constructions Loans [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	9,107,977	8,791,394
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	4,856,916	4,664,426
Commercial - industrial, financial, and agricultural
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	3,712,974	3,612,065
Commercial - Secured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	3,494,959	3,413,444
Commercial - Unsecured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	218,015	198,621
Construction, Excluding Contstruction Other [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	538,087	514,903
Construction - Commercial Residential [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	269,972	288,553
Construction - Commercial [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	268,115	226,350
Pass [Member] | Commercial Loans, Commercial Mortgages, Constructions Loans [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	8,317,249	7,891,757
Percentage of total loans rated	91.30%	89.80%
Pass [Member] | Real-estate commercial mortage [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	4,472,005	4,255,334
Pass [Member] | Commercial - industrial, financial, and agricultural
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	3,431,930	3,268,415
Pass [Member] | Commercial - Secured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	3,223,539	3,081,215
Pass [Member] | Commercial - Unsecured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	208,391	187,200
Pass [Member] | Construction, Excluding Contstruction Other [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	413,314	368,008
Pass [Member] | Construction - Commercial Residential [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	156,942	156,538
Pass [Member] | Construction - Commercial [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	256,372	211,470
Special Mention [Member] | Commercial Loans, Commercial Mortgages, Constructions Loans [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	321,066	355,571
Percentage of total loans rated	3.50%	4.00%
Special Mention [Member] | Real-estate commercial mortage [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	165,936	157,640
Special Mention [Member] | Commercial - industrial, financial, and agricultural
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	102,907	142,698
Special Mention [Member] | Commercial - Secured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	99,025	137,277
Special Mention [Member] | Commercial - Unsecured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	3,882	5,421
Special Mention [Member] | Construction, Excluding Contstruction Other [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	52,223	55,233
Special Mention [Member] | Construction - Commercial Residential [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	49,934	52,434
Special Mention [Member] | Construction - Commercial [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	2,289	2,799
Substandard [Member] | Commercial Loans, Commercial Mortgages, Constructions Loans [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	469,662	544,066
Percentage of total loans rated	5.20%	6.20%
Substandard [Member] | Real-estate commercial mortage [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	218,975	251,452
Substandard [Member] | Commercial - industrial, financial, and agricultural
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	178,137	200,952
Substandard [Member] | Commercial - Secured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	172,395	194,952
Substandard [Member] | Commercial - Unsecured [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	5,742	6,000
Substandard [Member] | Construction, Excluding Contstruction Other [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	72,550	91,662
Substandard [Member] | Construction - Commercial Residential [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	63,096	79,581
Substandard [Member] | Construction - Commercial [Member]
Internal risk ratings for loans by segment [Line Items]
Loans, gross of unearned income	$ 9,454	$ 12,081