Loans and Allowance for Credit Losses Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	$ 169,054	$ 184,144
Loans charged off	(33,927)	(32,157)	$ (44,593)
Recoveries of loans previously charged off	20,658	15,388	13,107
Loans Charged Off, Net Of Recoveries	(13,269)	(16,769)	(31,486)
Provision for loan losses	12,894	1,679
Financing receivable, allowance for credit losses, collectively evaluated for impairment	121,562	117,464
Financing receivable, allowance for credit losses, individually evaluated for impairment	47,117	51,590
Loans and Leases Receivable, Allowance, Ending Balance	168,679	169,054	184,144
Measured for impairment under FASB ASC Subtopic 450-20	14,519,579	13,648,521
Evaluated for impairment under FASB ASC Section 310-10-35	179,693	190,081
Loans, net of unearned income	14,699,272	13,838,602
Change in provision allocated to commitments to lend to borrowers	288	570
Provision for credit losses	13,182	2,250	12,500
Real estate – commercial mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	47,866	53,493
Loans charged off	(3,580)	(4,218)
Recoveries of loans previously charged off	3,373	2,801
Loans Charged Off, Net Of Recoveries	(207)	(1,417)
Provision for loan losses	(817)	(4,210)
Financing receivable, allowance for credit losses, collectively evaluated for impairment	36,680	35,395
Financing receivable, allowance for credit losses, individually evaluated for impairment	10,162	12,471
Loans and Leases Receivable, Allowance, Ending Balance	46,842	47,866	53,493
Measured for impairment under FASB ASC Subtopic 450-20	5,963,689	5,404,036
Evaluated for impairment under FASB ASC Section 310-10-35	54,893	58,294
Loans, net of unearned income	6,018,582	5,462,330
Commercial – industrial, financial and agricultural
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	57,098	51,378
Loans charged off	(15,276)	(15,639)
Recoveries of loans previously charged off	8,981	5,264
Loans Charged Off, Net Of Recoveries	(6,295)	(10,375)
Provision for loan losses	3,550	16,095
Financing receivable, allowance for credit losses, collectively evaluated for impairment	40,700	42,515
Financing receivable, allowance for credit losses, individually evaluated for impairment	13,653	14,583
Loans and Leases Receivable, Allowance, Ending Balance	54,353	57,098	51,378
Measured for impairment under FASB ASC Subtopic 450-20	4,038,511	4,040,810
Evaluated for impairment under FASB ASC Section 310-10-35	48,975	48,152
Loans, net of unearned income	4,087,486	4,088,962
Real estate – home equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	22,405	28,271
Loans charged off	(4,912)	(3,604)
Recoveries of loans previously charged off	1,171	1,362
Loans Charged Off, Net Of Recoveries	(3,741)	(2,242)
Provision for loan losses	8,137	(3,624)
Financing receivable, allowance for credit losses, collectively evaluated for impairment	17,290	14,412
Financing receivable, allowance for credit losses, individually evaluated for impairment	9,511	7,993
Loans and Leases Receivable, Allowance, Ending Balance	26,801	22,405	28,271
Measured for impairment under FASB ASC Subtopic 450-20	1,605,910	1,668,673
Evaluated for impairment under FASB ASC Section 310-10-35	19,205	15,766
Loans, net of unearned income	1,625,115	1,684,439
Real estate – residential mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	21,375	29,072
Loans charged off	(2,326)	(3,612)
Recoveries of loans previously charged off	1,072	1,322
Loans Charged Off, Net Of Recoveries	(1,254)	(2,290)
Provision for loan losses	2,808	(5,407)
Financing receivable, allowance for credit losses, collectively evaluated for impairment	11,032	7,953
Financing receivable, allowance for credit losses, individually evaluated for impairment	11,897	13,422
Loans and Leases Receivable, Allowance, Ending Balance	22,929	21,375	29,072
Measured for impairment under FASB ASC Subtopic 450-20	1,555,946	1,325,735
Evaluated for impairment under FASB ASC Section 310-10-35	46,048	50,425
Loans, net of unearned income	1,601,994	1,376,160
Real estate – construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	6,529	9,756
Loans charged off	(1,218)	(201)
Recoveries of loans previously charged off	3,924	2,824
Loans Charged Off, Net Of Recoveries	2,706	2,623
Provision for loan losses	(2,780)	(5,850)
Financing receivable, allowance for credit losses, collectively evaluated for impairment	4,587	4,134
Financing receivable, allowance for credit losses, individually evaluated for impairment	1,868	2,395
Loans and Leases Receivable, Allowance, Ending Balance	6,455	6,529	9,756
Measured for impairment under FASB ASC Subtopic 450-20	833,117	784,002
Evaluated for impairment under FASB ASC Section 310-10-35	10,532	15,986
Loans, net of unearned income	843,649	799,988
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	2,585	3,015
Loans charged off	(2,800)	(2,227)
Recoveries of loans previously charged off	1,295	1,130
Loans Charged Off, Net Of Recoveries	(1,505)	(1,097)
Provision for loan losses	2,494	667
Financing receivable, allowance for credit losses, collectively evaluated for impairment	3,548	2,563
Financing receivable, allowance for credit losses, individually evaluated for impairment	26	22
Loans and Leases Receivable, Allowance, Ending Balance	3,574	2,585	3,015
Measured for impairment under FASB ASC Subtopic 450-20	291,430	268,555
Evaluated for impairment under FASB ASC Section 310-10-35	40	33
Loans, net of unearned income	291,470	268,588
Leasing and other and overdrafts
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	2,468	1,799
Loans charged off	(3,815)	(2,656)
Recoveries of loans previously charged off	842	685
Loans Charged Off, Net Of Recoveries	(2,973)	(1,971)
Provision for loan losses	3,697	2,640
Financing receivable, allowance for credit losses, collectively evaluated for impairment	3,192	1,764
Financing receivable, allowance for credit losses, individually evaluated for impairment	0	704
Loans and Leases Receivable, Allowance, Ending Balance	3,192	2,468	1,799
Measured for impairment under FASB ASC Subtopic 450-20	230,976	156,710
Evaluated for impairment under FASB ASC Section 310-10-35	0	1,425
Loans, net of unearned income	230,976	158,135
Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance, Beginning Balance	8,728	7,360
Loans charged off	0	0
Recoveries of loans previously charged off		0
Loans Charged Off, Net Of Recoveries	0	0
Provision for loan losses	(4,195)	1,368
Financing receivable, allowance for credit losses, collectively evaluated for impairment	4,533	8,728
Loans and Leases Receivable, Allowance, Ending Balance	$ 4,533	$ 8,728	$ 7,360