Loans and Leases and the Allowance for Loan and Lease Losses (Credit Quality Indicators & Narrative) (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	$ 9,796,947	$ 8,949,785	$ 7,878,985
Classified
Recorded investment in loans and leases by class and by credit quality indicator
Number of months up to which residential and home equity loans may be considered classified, even if they are current as to principal and interest (in months)	6 months
Residential Mortgage | Classified
Recorded investment in loans and leases by class and by credit quality indicator
Maximum current loan-to-value ratio for residential mortgage and home equity loans to be considered as pass (as a percent)	60.00%
Home Equity | Classified
Recorded investment in loans and leases by class and by credit quality indicator
Maximum current loan-to-value ratio for residential mortgage and home equity loans to be considered as pass (as a percent)	60.00%
Commercial
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	$ 3,766,498	3,617,692	3,153,852
Commercial | Pass
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	3,660,931	3,466,817
Commercial | Special Mention
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	51,173	91,210
Commercial | Classified
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	54,394	59,665
Commercial | Commercial and Industrial
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	1,279,347	1,249,791
Commercial | Commercial and Industrial | Pass
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	1,234,738	1,203,025
Commercial | Commercial and Industrial | Special Mention
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	15,394	20,253
Commercial | Commercial and Industrial | Classified
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	29,215	26,513
Commercial | Commercial Mortgage
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	2,103,967	1,889,551
Commercial | Commercial Mortgage | Pass
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	2,046,745	1,792,119
Commercial | Commercial Mortgage | Special Mention
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	35,762	66,734
Commercial | Commercial Mortgage | Classified
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	21,460	30,698
Commercial | Construction
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	202,253	270,018
Commercial | Construction | Pass
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	198,926	264,287
Commercial | Construction | Special Mention
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	6	4,218
Commercial | Construction | Classified
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	3,321	1,513
Commercial | Lease Financing
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	180,931	208,332
Commercial | Lease Financing | Pass
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	180,522	207,386
Commercial | Lease Financing | Special Mention
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	11	5
Commercial | Lease Financing | Classified
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	398	941
Consumer
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	6,030,449	5,332,093	$ 4,725,133
Consumer | Pass
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	$ 6,015,043	5,310,202
Consumer | Special Mention
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases		2,964
Consumer | Classified
Recorded investment in loans and leases by class and by credit quality indicator
Number of days past due for loans and leases in classified credit quality indicator	90 days
Total Recorded Investment in Loans and Leases	$ 15,406	18,927
Consumer | Residential Mortgage
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	3,466,773	3,163,073
Consumer | Residential Mortgage | Pass
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	$ 3,457,531	3,149,294
Consumer | Residential Mortgage | Special Mention
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases		0
Consumer | Residential Mortgage | Classified
Recorded investment in loans and leases by class and by credit quality indicator
Number of days past due for loans and leases in classified credit quality indicator	90 days
Total Recorded Investment in Loans and Leases	$ 9,242	13,779
Consumer | Home Equity
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	1,585,455	1,334,163
Consumer | Home Equity | Pass
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	$ 1,580,917	1,327,676
Consumer | Home Equity | Special Mention
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases		2,964
Consumer | Home Equity | Classified
Recorded investment in loans and leases by class and by credit quality indicator
Number of days past due for loans and leases in classified credit quality indicator	90 days
Total Recorded Investment in Loans and Leases	$ 4,538	3,523
Consumer | Automobile
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	528,474	454,333
Consumer | Automobile | Pass
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	527,587	453,439
Consumer | Automobile | Special Mention
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases		0
Consumer | Automobile | Classified
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	887	894
Consumer | Other
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	449,747	380,524
Consumer | Other | Pass
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	449,008	379,793
Consumer | Other | Special Mention
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases		0
Consumer | Other | Classified
Recorded investment in loans and leases by class and by credit quality indicator
Total Recorded Investment in Loans and Leases	$ 739	$ 731