Loans and Allowance for Loan Losses (Loan Portfolio Credit Exposure) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 23,088,535	$ 22,459,664	$ 21,523,990
Accrual substandard loans	270,100	303,700
Deferred fees and costs, net	$ 27,600	30,100	$ 29,100
Maximum [Member]
Financing Receivable, Recorded Investment [Line Items]
Allowance for loan losses, percent of loan amount	50.00%
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 7,507,695	7,394,768
Investment Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,920,661	5,751,631
1-4 Family Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,127,780	1,129,156
Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	459,254	513,981
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,955,430	10,772,130
Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,596,835	6,453,180
Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,358,595	4,318,950
Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,625,410	4,292,766
Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,657,109	1,689,914
Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,132,114	1,938,683
Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	236,034	240,851
Other Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	600,153	423,318
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	22,229,181	21,531,712
Pass [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,185,131	6,993,333
Pass [Member] | Investment Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,788,229	5,560,595
Pass [Member] | 1-4 Family Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,009,820	995,903
Pass [Member] | Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	387,082	436,835
Pass [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,478,259	10,302,810
Pass [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,317,597	6,184,179
Pass [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,160,662	4,118,631
Pass [Member] | Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,565,791	4,235,569
Pass [Member] | Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,632,841	1,666,586
Pass [Member] | Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,102,767	1,910,649
Pass [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	234,728	239,405
Pass [Member] | Other Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	595,455	418,929
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	435,231	455,917
Special Mention [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	190,101	225,238
Special Mention [Member] | Investment Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	86,101	114,705
Special Mention [Member] | 1-4 Family Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	51,938	64,325
Special Mention [Member] | Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	52,062	46,208
Special Mention [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	245,130	230,679
Special Mention [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	163,494	152,189
Special Mention [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	81,636	78,490
Special Mention [Member] | Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
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
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	399,189	441,853
Substandard [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	124,904	168,631
Substandard [Member] | Investment Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	46,331	76,331
Substandard [Member] | 1-4 Family Properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	58,789	61,726
Substandard [Member] | Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	19,784	30,574
Substandard [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	219,516	221,930
Substandard [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	105,107	100,658
Substandard [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	114,409	121,272
Substandard [Member] | Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	54,769	51,292
Substandard [Member] | Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,808	20,456
Substandard [Member] | Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	27,808	26,041
Substandard [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	533	480
Substandard [Member] | Other Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,620	4,315
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,952	23,900
Doubtful [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,559	7,566
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	7,233	7,202
Doubtful [Member] | Land Acquisition [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	326	364
Doubtful [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,820	13,428
Doubtful [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,400	13,330
Doubtful [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,420	98
Doubtful [Member] | Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,573	2,906
Doubtful [Member] | Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,201	1,206
Doubtful [Member] | Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,372	1,700
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	0
Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,982	6,282
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 and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	705	3,283
Loss [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	237	2,824
Loss [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	468	459
Loss [Member] | Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,277	2,999
Loss [Member] | Home Equity Lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,259	1,666
Loss [Member] | Consumer Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	167	293
Loss [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	773	966
Loss [Member] | Other Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 78	$ 74