Loans and Allowance for Credit Losses Allowance for Loan Losses by Portfolio Segment (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	$ 202,780	$ 223,903
Loans charged off	(44,593)	(80,212)	(140,366)
Loans Charged Off, Net Of Recoveries	(31,486)	(61,022)	(126,738)
Provision for loan losses	12,850	39,899
Loans and Leases Receivable, Allowance, Ending Balance	184,144	202,780	223,903
Change in provision allocated to commitments to lend to borrowers	350	601
Financing receivable, allowance for credit losses, collectively evaluated for impairment	123,277	139,582
Financing receivable, allowance for credit losses, individually evaluated for impairment	60,867	63,198
Loans, net of unearned income	13,111,716	12,782,220
Real estate – commercial mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	55,659	62,928
Loans charged off	(6,004)	(20,829)
Loans Charged Off, Net Of Recoveries	(4,044)	(17,335)
Provision for loan losses	1,878	10,066
Loans and Leases Receivable, Allowance, Ending Balance	53,493	55,659
Financing receivable, allowance for credit losses, collectively evaluated for impairment	36,778	41,215
Financing receivable, allowance for credit losses, individually evaluated for impairment	16,715	14,444
Loans, net of unearned income	5,197,155	5,101,922
Commercial – industrial, financial and agricultural
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	50,330	60,205
Loans charged off	(24,516)	(30,383)
Loans Charged Off, Net Of Recoveries	(20,260)	(21,102)
Provision for loan losses	21,308	11,227
Loans and Leases Receivable, Allowance, Ending Balance	51,378	50,330
Financing receivable, allowance for credit losses, collectively evaluated for impairment	38,348	36,263
Financing receivable, allowance for credit losses, individually evaluated for impairment	13,030	14,067
Loans, net of unearned income	3,725,567	3,628,420
Real estate – home equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	28,222	22,776
Loans charged off	(5,486)	(8,193)
Loans Charged Off, Net Of Recoveries	(4,461)	(7,333)
Provision for loan losses	4,510	12,779
Loans and Leases Receivable, Allowance, Ending Balance	28,271	28,222
Financing receivable, allowance for credit losses, collectively evaluated for impairment	19,047	19,163
Financing receivable, allowance for credit losses, individually evaluated for impairment	9,224	9,059
Loans, net of unearned income	1,736,688	1,764,197
Real estate – residential mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	33,082	34,536
Loans charged off	(2,918)	(9,705)
Loans Charged Off, Net Of Recoveries	(2,467)	(9,157)
Provision for loan losses	(1,543)	7,703
Loans and Leases Receivable, Allowance, Ending Balance	29,072	33,082
Financing receivable, allowance for credit losses, collectively evaluated for impairment	10,480	11,337
Financing receivable, allowance for credit losses, individually evaluated for impairment	18,592	21,745
Loans, net of unearned income	1,377,068	1,337,380
Real estate – construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	12,649	17,287
Loans charged off	(1,209)	(6,572)
Loans Charged Off, Net Of Recoveries	1,968	(3,890)
Provision for loan losses	(4,861)	(748)
Loans and Leases Receivable, Allowance, Ending Balance	9,756	12,649
Financing receivable, allowance for credit losses, collectively evaluated for impairment	6,485	8,778
Financing receivable, allowance for credit losses, individually evaluated for impairment	3,271	3,871
Loans, net of unearned income	690,601	573,672
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	3,260	2,367
Loans charged off	(2,325)	(1,877)
Loans Charged Off, Net Of Recoveries	(1,003)	(359)
Provision for loan losses	758	1,252
Loans and Leases Receivable, Allowance, Ending Balance	3,015	3,260
Financing receivable, allowance for credit losses, collectively evaluated for impairment	2,980	3,248
Financing receivable, allowance for credit losses, individually evaluated for impairment	35	12
Loans, net of unearned income	265,431	283,124
Leasing and other and overdrafts
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	3,370	2,752
Loans charged off	(2,135)	(2,653)
Loans Charged Off, Net Of Recoveries	(1,219)	(1,846)
Provision for loan losses	(352)	2,464
Loans and Leases Receivable, Allowance, Ending Balance	1,799	3,370
Financing receivable, allowance for credit losses, collectively evaluated for impairment	1,799	3,370
Financing receivable, allowance for credit losses, individually evaluated for impairment	0	0
Loans, net of unearned income	119,206	93,505
Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	16,208	21,052
Loans charged off	0	0
Loans Charged Off, Net Of Recoveries	0	0
Provision for loan losses	(8,848)	(4,844)
Loans and Leases Receivable, Allowance, Ending Balance	7,360	16,208
Financing receivable, allowance for credit losses, collectively evaluated for impairment	$ 7,360	$ 16,208