Loans and Allowance for Loan Losses (Loan Portfolio Credit Exposure) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 21,523,990	$ 21,128,489	$ 20,484,718
Nonaccrual substandard loans	146,300	170,900
Deferred fees and costs, net	$ 29,100	30,800	$ 29,000
Maximum [Member]
Financing Receivable, Recorded Investment [Line Items]
Allowance for loan losses, percent of loan amount	50.00%
Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 1,683,651	1,683,998
Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,793,752	1,694,061
Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	246,724	253,649
Other Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	323,741	302,460
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,400,322	10,257,429
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,075,800	6,936,892
Investment Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,423,893	5,216,964
1-4 Family Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,097,406	1,133,882
Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	554,501	586,046
Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,259,553	6,182,312
Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,140,769	4,075,117
Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,047,868	3,934,168
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	20,434,333	19,940,436
Pass [Member] | Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,657,790	1,659,794
Pass [Member] | Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,759,349	1,653,491
Pass [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	245,357	252,275
Pass [Member] | Other Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	319,932	298,991
Pass [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,863,774	9,723,242
Pass [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,588,131	6,352,643
Pass [Member] | Investment Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,184,993	4,946,609
Pass [Member] | 1-4 Family Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	944,376	943,721
Pass [Member] | Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	458,762	462,313
Pass [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,959,330	5,905,589
Pass [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,904,444	3,817,653
Pass [Member] | Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,982,428	3,864,551
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	522,863	553,990
Special Mention [Member] | Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Special Mention [Member] | Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Special Mention [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Special Mention [Member] | Other Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Special Mention [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	256,474	239,526
Special Mention [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	266,389	314,464
Special Mention [Member] | Investment Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	151,839	167,490
Special Mention [Member] | 1-4 Family Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	65,752	86,072
Special Mention [Member] | Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	48,798	60,902
Special Mention [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	159,282	143,879
Special Mention [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	97,192	95,647
Special Mention [Member] | Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	539,501	607,161
Substandard [Member] | Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	22,471	20,043
Substandard [Member] | Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	32,685	37,656
Substandard [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	427	495
Substandard [Member] | Other Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,667	3,339
Substandard [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	268,051	284,270
Substandard [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	212,200	261,358
Substandard [Member] | Investment Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	87,061	102,865
Substandard [Member] | 1-4 Family Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	78,648	96,392
Substandard [Member] | Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	46,491	62,101
Substandard [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	129,704	123,225
Substandard [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	138,347	161,045
Substandard [Member] | Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	59,250	61,533
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	23,141	22,988
Doubtful [Member] | Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,762	2,009
Doubtful [Member] | Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,593	2,654
Doubtful [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Doubtful [Member] | Other Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	56	32
Doubtful [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,650	9,866
Doubtful [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,080	8,427
Doubtful [Member] | Investment Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Doubtful [Member] | 1-4 Family Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,630	7,697
Doubtful [Member] | Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	450	730
Doubtful [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,323	9,539
Doubtful [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	327	327
Doubtful [Member] | Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,411	4,695
Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,152	3,914
Loss [Member] | Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,628	2,152
Loss [Member] | Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	125	260
Loss [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	940	879
Loss [Member] | Other Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	86	98
Loss [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,373	525
Loss [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loss [Member] | Investment Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loss [Member] | 1-4 Family Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loss [Member] | Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loss [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	914	80
Loss [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	459	445
Loss [Member] | Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 2,779	$ 3,389