Loans and Allowance for Credit Losses Summary of Delinquency and Non-Performing Status by Portfolio Segment (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) day	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	$ 15,792,969	$ 15,768,247	$ 15,346,617
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	$ 1,491,395	1,559,719	1,579,739
Real-estate - home equity | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	1,470,006	1,535,557
Real-estate - home equity | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	9,703	12,655
Real-estate - home equity | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	11,686	11,507
Real estate - residential mortgage
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	2,094,530	1,954,711	1,784,712
Real estate - residential mortgage | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	2,054,810	1,914,888
Real estate - residential mortgage | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	20,832	18,852
Real estate - residential mortgage | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	18,888	20,971
Construction - other
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	78,993	78,017
Construction - other | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	78,503	77,403
Construction - other | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	0	203
Construction - other | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	490	411
Consumer
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	62,333	55,213
Consumer | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	62,142	54,828
Consumer | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	108	315
Consumer | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	83	70
Consumer - indirect
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	297,982	258,570
Consumer - indirect | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	294,686	254,663
Consumer - indirect | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	3,027	3,681
Consumer - indirect | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	269	226
Consumer
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	360,315	313,783	283,156
Consumer | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	356,828	309,491
Consumer | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	3,135	3,996
Consumer | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	352	296
Leasing, other and overdrafts
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	286,947	267,998	$ 252,253
Leasing, other and overdrafts | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	285,722	267,111
Leasing, other and overdrafts | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	1,049	855
Leasing, other and overdrafts | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	176	32
Real Estate, Consumer, Leasing And Other Loans [Member] [Member]
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	4,312,180	4,174,228
Real Estate, Consumer, Leasing And Other Loans [Member] [Member] | Performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	4,245,869	4,104,450
Real Estate, Consumer, Leasing And Other Loans [Member] [Member] | Delinquent
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	34,719	36,561
Real Estate, Consumer, Leasing And Other Loans [Member] [Member] | Non-performing
Financing Receivable, Impaired [Line Items]
Loans, net of unearned income	$ 31,592	$ 33,217
Commercial Loans, Commerical Mortgages, Constructions Loans
Financing Receivable, Impaired [Line Items]
% of Total	100.00%	100.00%
Commercial Loans, Commerical Mortgages, Constructions Loans | Performing
Financing Receivable, Impaired [Line Items]
% of Total	98.50%	98.30%
Commercial Loans, Commerical Mortgages, Constructions Loans | Delinquent
Financing Receivable, Impaired [Line Items]
% of Total	0.80%	0.90%
Commercial Loans, Commerical Mortgages, Constructions Loans | Non-performing
Financing Receivable, Impaired [Line Items]
% of Total	0.70%	0.80%