Loans And Allowance For Loan Losses (Loan Portfolio Credit Exposure) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 24,812,795	$ 23,882,382
Performing, accrual of interest	190,600	256,600
Deferred fees and costs, net	25,331	25,991	$ 30,100
Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,935,288	7,374,112
Total commercial real estate | Investment properties
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,670,065	5,869,261
Total commercial real estate | 1-4 family properties
Financing Receivable, Recorded Investment [Line Items]
Total loans	781,619	888,553
Total commercial real estate | Land and development
Financing Receivable, Recorded Investment [Line Items]
Total loans	483,604	616,298
Total commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,023,650	11,543,806
Total commercial and industrial | Commercial, financial and agricultural
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,179,487	6,909,036
Total commercial and industrial | Owner-occupied
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,844,163	4,634,770
Total consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 5,853,857	4,964,464
Allowance for loan and lease losses, percent of loan amount	50.00%
Total consumer | Home equity lines
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 1,514,227	1,617,265
Total consumer | Consumer mortgages
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,633,503	2,296,604
Total consumer | Credit cards
Financing Receivable, Recorded Investment [Line Items]
Total loans	232,676	232,413
Total consumer | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,473,451	818,182
Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	24,222,726	23,147,814
Pass | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,763,850	7,143,928
Pass | Total commercial real estate | Investment properties
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,586,792	5,794,626
Pass | Total commercial real estate | 1-4 family properties
Financing Receivable, Recorded Investment [Line Items]
Total loans	745,299	827,557
Pass | Total commercial real estate | Land and development
Financing Receivable, Recorded Investment [Line Items]
Total loans	431,759	521,745
Pass | Total commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,643,383	11,096,931
Pass | Total commercial and industrial | Commercial, financial and agricultural
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,929,506	6,635,757
Pass | Total commercial and industrial | Owner-occupied
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,713,877	4,461,174
Pass | Total consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,815,493	4,906,955
Pass | Total consumer | Home equity lines
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,491,105	1,589,199
Pass | Total consumer | Consumer mortgages
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,622,499	2,271,916
Pass | Total consumer | Credit cards
Financing Receivable, Recorded Investment [Line Items]
Total loans	230,945	230,997
Pass | Total consumer | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,470,944	814,843
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	283,865	324,593
Special Mention | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	117,813	137,469
Special Mention | Total commercial real estate | Investment properties
Financing Receivable, Recorded Investment [Line Items]
Total loans	64,628	43,336
Special Mention | Total commercial real estate | 1-4 family properties
Financing Receivable, Recorded Investment [Line Items]
Total loans	19,419	33,928
Special Mention | Total commercial real estate | Land and development
Financing Receivable, Recorded Investment [Line Items]
Total loans	33,766	60,205
Special Mention | Total commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total loans	166,052	187,124
Special Mention | Total commercial and industrial | Commercial, financial and agricultural
Financing Receivable, Recorded Investment [Line Items]
Total loans	115,912	126,268
Special Mention | Total commercial and industrial | Owner-occupied
Financing Receivable, Recorded Investment [Line Items]
Total loans	50,140	60,856
Special Mention | Total consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Special Mention | Total consumer | Home equity lines
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Special Mention | Total consumer | Consumer mortgages
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Special Mention | Total consumer | Credit cards
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Special Mention | Total consumer | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	297,640	387,117
Substandard | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	50,496	85,450
Substandard | Total commercial real estate | Investment properties
Financing Receivable, Recorded Investment [Line Items]
Total loans	18,645	31,299
Substandard | Total commercial real estate | 1-4 family properties
Financing Receivable, Recorded Investment [Line Items]
Total loans	16,901	26,790
Substandard | Total commercial real estate | Land and development
Financing Receivable, Recorded Investment [Line Items]
Total loans	14,950	27,361
Substandard | Total commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total loans	212,891	251,755
Substandard | Total commercial and industrial | Commercial, financial and agricultural
Financing Receivable, Recorded Investment [Line Items]
Total loans	132,818	140,425
Substandard | Total commercial and industrial | Owner-occupied
Financing Receivable, Recorded Investment [Line Items]
Total loans	80,073	111,330
Substandard | Total consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	34,253	49,912
Substandard | Total consumer | Home equity lines
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,079	22,774
Substandard | Total consumer | Consumer mortgages
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,607	23,268
Substandard | Total consumer | Credit cards
Financing Receivable, Recorded Investment [Line Items]
Total loans	399	637
Substandard | Total consumer | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,168	3,233
Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,358	19,337
Doubtful | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,129	7,265
Doubtful | Total commercial real estate | Investment properties
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Doubtful | Total commercial real estate | 1-4 family properties
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	278
Doubtful | Total commercial real estate | Land and development
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,129	6,987
Doubtful | Total commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,324	7,855
Doubtful | Total commercial and industrial | Commercial, financial and agricultural
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,251	6,445
Doubtful | Total commercial and industrial | Owner-occupied
Financing Receivable, Recorded Investment [Line Items]
Total loans	73	1,410
Doubtful | Total consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	905	4,217
Doubtful | Total consumer | Home equity lines
Financing Receivable, Recorded Investment [Line Items]
Total loans	285	2,892
Doubtful | Total consumer | Consumer mortgages
Financing Receivable, Recorded Investment [Line Items]
Total loans	291	1,283
Doubtful | Total consumer | Credit cards
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Doubtful | Total consumer | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	329	42
Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,206	3,521
Loss | Total commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loss | Total commercial real estate | Investment properties
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loss | Total commercial real estate | 1-4 family properties
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loss | Total commercial real estate | Land and development
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loss | Total commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	141
Loss | Total commercial and industrial | Commercial, financial and agricultural
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	141
Loss | Total commercial and industrial | Owner-occupied
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loss | Total consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,206	3,380
Loss | Total consumer | Home equity lines
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,758	2,400
Loss | Total consumer | Consumer mortgages
Financing Receivable, Recorded Investment [Line Items]
Total loans	106	137
Loss | Total consumer | Credit cards
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,332	779
Loss | Total consumer | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 10	$ 64