Loans and Allowance for Credit Losses Summary of Delinquency and Non-Performing Status by Portfolio Segment (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($) day	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	$ 15,486,899	$ 14,699,272	$ 14,391,238
Delinquent | Minimum
Financing Receivable, Impaired [Line Items]
Days past due | day	30
Delinquent | Maximum
Financing Receivable, Impaired [Line Items]
Days past due | day	89
Non-performing
Financing Receivable, Impaired [Line Items]
Days past due | day	90
Real-estate - home equity
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	$ 1,567,473	1,625,115	1,640,421
Real-estate - home equity | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	1,542,289	1,602,687
Real-estate - home equity | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	12,955	9,274
Real-estate - home equity | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	12,229	13,154
Real estate - residential mortgage
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	1,887,907	1,601,994	1,542,696
Real estate - residential mortgage | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	1,845,495	1,557,995
Real estate - residential mortgage | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	20,769	20,344
Real estate - residential mortgage | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	21,643	23,655
Construction - other
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	65,583	56,970
Construction - other | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	64,110	55,874
Construction - other | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	382	0
Construction - other | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	1,091	1,096
Consumer - direct
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	55,711	96,887
Consumer - direct | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	55,490	93,572
Consumer - direct | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	158	1,752
Consumer - direct | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	63	1,563
Consumer - indirect
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	246,737	194,583
Consumer - indirect | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	243,723	190,656
Consumer - indirect | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	2,834	3,599
Consumer - indirect | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	180	328
Consumer
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	302,448	291,470	283,673
Consumer | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	299,213	284,228
Consumer | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	2,992	5,351
Consumer | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	243	1,891
Leasing, other and overdrafts
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	257,748	230,976	$ 219,780
Leasing, other and overdrafts | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	256,784	229,591
Leasing, other and overdrafts | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	884	1,068
Leasing, other and overdrafts | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	80	317
Commercial Loans, Commerical Mortgages, Constructions Loans
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	$ 4,081,159	$ 3,806,525
% of Total	100.00%	100.00%
Commercial Loans, Commerical Mortgages, Constructions Loans | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	$ 4,007,891	$ 3,730,375
% of Total	98.20%	98.00%
Commercial Loans, Commerical Mortgages, Constructions Loans | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	$ 37,982	$ 36,037
% of Total	0.90%	0.90%
Commercial Loans, Commerical Mortgages, Constructions Loans | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	$ 35,286	$ 40,113
% of Total	0.90%	1.10%