Loans and Allowance for Loan Losses (Loan Portfolio Credit Exposure) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 21,892,675	$ 21,128,489	$ 20,617,415
Nonaccrual substandard loans	126,600	170,900
Deferred fees and costs, net	$ 28,400	30,800	$ 28,800
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	$ 1,684,047	1,683,998
Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,888,456	1,694,061
Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	241,315	253,649
Other Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	345,425	302,460
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,543,176	10,267,719
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,190,256	6,926,602
Investment Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,557,576	5,206,674
1-4 Family Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,094,553	1,133,882
Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	538,127	586,046
Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,277,768	6,182,312
Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,265,408	4,085,407
Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,159,243	3,934,168
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	20,922,357	19,940,436
Pass [Member] | Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,659,346	1,659,794
Pass [Member] | Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,858,377	1,653,491
Pass [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	239,992	252,275
Pass [Member] | Other Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	341,584	298,991
Pass [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,061,201	9,733,532
Pass [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,761,857	6,342,353
Pass [Member] | Investment Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,357,016	4,936,319
Pass [Member] | 1-4 Family Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	953,403	943,721
Pass [Member] | Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	451,438	462,313
Pass [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,001,990	5,905,589
Pass [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,059,211	3,827,943
Pass [Member] | Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,099,299	3,864,551
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	454,892	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	218,775	239,526
Special Mention [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	236,117	314,464
Special Mention [Member] | Investment Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	125,646	167,490
Special Mention [Member] | 1-4 Family Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	58,314	86,072
Special Mention [Member] | Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	52,157	60,902
Special Mention [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	141,305	143,879
Special Mention [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	77,470	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	484,407	607,161
Substandard [Member] | Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,758	20,043
Substandard [Member] | Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	28,460	37,656
Substandard [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	497	495
Substandard [Member] | Other Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,761	3,339
Substandard [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	245,347	284,270
Substandard [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	184,584	261,358
Substandard [Member] | Investment Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	74,914	102,865
Substandard [Member] | 1-4 Family Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	75,586	96,392
Substandard [Member] | Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	34,084	62,101
Substandard [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	117,256	123,225
Substandard [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	128,091	161,045
Substandard [Member] | Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	54,476	61,533
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	26,606	22,988
Doubtful [Member] | Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,448	2,009
Doubtful [Member] | Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,494	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	0	32
Doubtful [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	15,966	9,866
Doubtful [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,698	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	7,250	7,697
Doubtful [Member] | Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	448	730
Doubtful [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	15,789	9,539
Doubtful [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	177	327
Doubtful [Member] | Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,942	4,695
Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,413	3,914
Loss [Member] | Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,495	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	826	879
Loss [Member] | Other Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	80	98
Loss [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,887	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	1,428	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	$ 2,526	$ 3,389