Loans and Allowance for Credit Losses Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	$ 184,144	$ 202,780
Loans charged off	(32,157)	(44,593)	$ (80,212)
Recoveries of loans previously charged off	15,388	13,107	19,190
Loans Charged Off, Net Of Recoveries	(16,769)	(31,486)	(61,022)
Provision for loan losses	1,679	12,850
Financing receivable, allowance for credit losses, collectively evaluated for impairment	117,464	123,277
Financing receivable, allowance for credit losses, individually evaluated for impairment	51,590	60,867
Loans and Leases Receivable, Allowance, Ending Balance	169,054	184,144	202,780
Measured for impairment under FASB ASC Subtopic 450-20	13,648,521	12,923,015
Evaluated for impairment under FASB ASC Section 310-10-35	190,081	188,701
Loans, net of unearned income	$ 13,838,602	$ 13,111,716
Percentage of Unallocated Allowance	5.00%	4.00%
Change in provision allocated to commitments to lend to borrowers	$ 571	$ 350
Provision for credit losses	2,250	12,500	40,500
Real estate – commercial mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	53,493	55,659
Loans charged off	(4,218)	(6,004)
Recoveries of loans previously charged off	2,801	1,960
Loans Charged Off, Net Of Recoveries	(1,417)	(4,044)
Provision for loan losses	(4,210)	1,878
Financing receivable, allowance for credit losses, collectively evaluated for impairment	35,395	36,778
Financing receivable, allowance for credit losses, individually evaluated for impairment	12,471	16,715
Loans and Leases Receivable, Allowance, Ending Balance	47,866	53,493	55,659
Measured for impairment under FASB ASC Subtopic 450-20	5,404,036	5,133,896
Evaluated for impairment under FASB ASC Section 310-10-35	58,294	63,259
Loans, net of unearned income	5,462,330	5,197,155
Commercial – industrial, financial and agricultural
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	51,378	50,330
Loans charged off	(15,639)	(24,516)
Recoveries of loans previously charged off	5,264	4,256
Loans Charged Off, Net Of Recoveries	(10,375)	(20,260)
Provision for loan losses	16,095	21,308
Financing receivable, allowance for credit losses, collectively evaluated for impairment	42,515	38,348
Financing receivable, allowance for credit losses, individually evaluated for impairment	14,583	13,030
Loans and Leases Receivable, Allowance, Ending Balance	57,098	51,378	50,330
Measured for impairment under FASB ASC Subtopic 450-20	4,040,810	3,690,561
Evaluated for impairment under FASB ASC Section 310-10-35	48,152	35,006
Loans, net of unearned income	4,088,962	3,725,567
Real estate – home equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	28,271	28,222
Loans charged off	(3,604)	(5,486)
Recoveries of loans previously charged off	1,362	1,025
Loans Charged Off, Net Of Recoveries	(2,242)	(4,461)
Provision for loan losses	(3,624)	4,510
Financing receivable, allowance for credit losses, collectively evaluated for impairment	14,412	19,047
Financing receivable, allowance for credit losses, individually evaluated for impairment	7,993	9,224
Loans and Leases Receivable, Allowance, Ending Balance	22,405	28,271	28,222
Measured for impairment under FASB ASC Subtopic 450-20	1,668,673	1,723,230
Evaluated for impairment under FASB ASC Section 310-10-35	15,766	13,458
Loans, net of unearned income	1,684,439	1,736,688
Real estate – residential mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	29,072	33,082
Loans charged off	(3,612)	(2,918)
Recoveries of loans previously charged off	1,322	451
Loans Charged Off, Net Of Recoveries	(2,290)	(2,467)
Provision for loan losses	(5,407)	(1,543)
Financing receivable, allowance for credit losses, collectively evaluated for impairment	7,953	10,480
Financing receivable, allowance for credit losses, individually evaluated for impairment	13,422	18,592
Loans and Leases Receivable, Allowance, Ending Balance	21,375	29,072	33,082
Measured for impairment under FASB ASC Subtopic 450-20	1,325,735	1,325,717
Evaluated for impairment under FASB ASC Section 310-10-35	50,425	51,351
Loans, net of unearned income	1,376,160	1,377,068
Real estate – construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	9,756	12,649
Loans charged off	(201)	(1,209)
Recoveries of loans previously charged off	2,824	3,177
Loans Charged Off, Net Of Recoveries	2,623	1,968
Provision for loan losses	(5,850)	(4,861)
Financing receivable, allowance for credit losses, collectively evaluated for impairment	4,134	6,485
Financing receivable, allowance for credit losses, individually evaluated for impairment	2,395	3,271
Loans and Leases Receivable, Allowance, Ending Balance	6,529	9,756	12,649
Measured for impairment under FASB ASC Subtopic 450-20	784,002	665,012
Evaluated for impairment under FASB ASC Section 310-10-35	15,986	25,589
Loans, net of unearned income	799,988	690,601
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	3,015	3,260
Loans charged off	(2,227)	(2,325)
Recoveries of loans previously charged off	1,130	1,322
Loans Charged Off, Net Of Recoveries	(1,097)	(1,003)
Provision for loan losses	667	758
Financing receivable, allowance for credit losses, collectively evaluated for impairment	2,563	2,980
Financing receivable, allowance for credit losses, individually evaluated for impairment	22	35
Loans and Leases Receivable, Allowance, Ending Balance	2,585	3,015	3,260
Measured for impairment under FASB ASC Subtopic 450-20	268,555	265,393
Evaluated for impairment under FASB ASC Section 310-10-35	33	38
Loans, net of unearned income	268,588	265,431
Leasing and other and overdrafts
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	1,799	3,370
Loans charged off	(2,656)	(2,135)
Recoveries of loans previously charged off	685	916
Loans Charged Off, Net Of Recoveries	(1,971)	(1,219)
Provision for loan losses	2,640	(352)
Financing receivable, allowance for credit losses, collectively evaluated for impairment	1,764	1,799
Financing receivable, allowance for credit losses, individually evaluated for impairment	704	0
Loans and Leases Receivable, Allowance, Ending Balance	2,468	1,799	3,370
Measured for impairment under FASB ASC Subtopic 450-20	156,710	119,206
Evaluated for impairment under FASB ASC Section 310-10-35	1,425	0
Loans, net of unearned income	158,135	119,206
Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	7,360	16,208
Loans charged off	0	0
Recoveries of loans previously charged off		0
Loans Charged Off, Net Of Recoveries	0	0
Provision for loan losses	1,368	(8,848)
Financing receivable, allowance for credit losses, collectively evaluated for impairment	8,728	7,360
Loans and Leases Receivable, Allowance, Ending Balance	$ 8,728	$ 7,360	$ 16,208