Allowance for Loan and Lease Losses - Credit Risk Profiles (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) factor	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Credit quality
Percentage of loans sold with no recourse not subject to grading	100.00%
Number of risk factors in internal loan rating system | factor	8
Loans and leases	$ 12,277,369	$ 11,520,378	$ 10,722,030
Loss
Credit quality
Loans and leases	0	0
Commercial Lending
Credit quality
Loans and leases	6,600,840	6,213,147
Commercial Lending | Pass
Credit quality
Loans and leases	6,445,576	6,089,637
Commercial Lending | Special mention
Credit quality
Loans and leases	73,876	69,735
Commercial Lending | Substandard
Credit quality
Loans and leases	79,674	51,856
Commercial Lending | Doubtful
Credit quality
Loans and leases	1,714	1,919
Commercial and Industrial
Credit quality
Loans and leases	3,135,266	3,239,600	3,057,455
Commercial and Industrial | Pass
Credit quality
Loans and leases	3,035,121	3,166,304
Commercial and Industrial | Special mention
Credit quality
Loans and leases	43,435	41,719
Commercial and Industrial | Substandard
Credit quality
Loans and leases	54,996	29,811
Commercial and Industrial | Doubtful
Credit quality
Loans and leases	1,714	1,766
Commercial Real Estate
Credit quality
Loans and leases	2,667,597	2,343,495	2,164,448
Commercial Real Estate | Pass
Credit quality
Loans and leases	2,619,494	2,298,839
Commercial Real Estate | Special mention
Credit quality
Loans and leases	26,248	23,859
Commercial Real Estate | Substandard
Credit quality
Loans and leases	21,855	20,797
Construction
Credit quality
Loans and leases	632,911	450,012	367,460
Construction | Pass
Credit quality
Loans and leases	628,112	445,149
Construction | Special mention
Credit quality
Loans and leases	2,377	3,789
Construction | Substandard
Credit quality
Loans and leases	2,422	1,074
Lease Financing
Credit quality
Loans and leases	165,066	180,040	198,679
Lease Financing | Pass
Credit quality
Loans and leases	162,849	179,345
Lease Financing | Special mention
Credit quality
Loans and leases	1,816	368
Lease Financing | Substandard
Credit quality
Loans and leases	401	174
Lease Financing | Doubtful
Credit quality
Loans and leases		153
Residential and consumer
Credit quality
Loans and leases	5,676,529	5,307,231
Residential and consumer | Performing
Credit quality
Loans and leases	5,630,723	5,265,885
Residential and consumer | Non-performing and delinquent
Credit quality
Loans and leases	45,806	41,346
Residential
Credit quality
Loans and leases	4,090,053	3,796,459	3,532,427
Residential | Performing
Credit quality
Loans and leases	4,073,834	3,778,070
Residential | Non-performing and delinquent
Credit quality
Loans and leases	16,219	18,389
Consumer
Credit quality
Loans and leases	1,586,476	1,510,772	$ 1,401,561
Consumer loans | Consumer
Credit quality
Loans and leases	234,358	243,512
Consumer loans | Consumer | Performing
Credit quality
Loans and leases	231,023	240,185
Consumer loans | Consumer | Non-performing and delinquent
Credit quality
Loans and leases	3,335	3,327
Consumer - Auto | Consumer
Credit quality
Loans and leases	1,023,697	922,756
Consumer - Auto | Consumer | Performing
Credit quality
Loans and leases	1,001,085	906,829
Consumer - Auto | Consumer | Non-performing and delinquent
Credit quality
Loans and leases	22,612	15,927
Credit Cards | Consumer
Credit quality
Loans and leases	328,421	344,504
Credit Cards | Consumer | Performing
Credit quality
Loans and leases	324,781	340,801
Credit Cards | Consumer | Non-performing and delinquent
Credit quality
Loans and leases	$ 3,640	$ 3,703