Loans and Leases and the Allowance for Loan and Lease Losses (Credit Quality Indicators & Narrative) (Details 3) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	$ 9,916,628	$ 9,796,947	$ 9,113,809
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	6 months
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
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
Number of days past due for loans and leases in classified credit quality indicator	90 days
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	$ 3,792,736	3,766,498	3,630,495
Commercial | Pass
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	3,692,898	3,660,931
Commercial | Special Mention
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	58,947	51,173
Commercial | Classified
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	40,891	54,394
Commercial | Commercial and Industrial
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	1,329,096	1,279,347
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	1,289,103	1,234,738
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	22,506	15,394
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	17,487	29,215
Commercial | Commercial Mortgage
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	2,097,339	2,103,967
Commercial | Commercial Mortgage | Pass
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	2,041,154	2,046,745
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	36,431	35,762
Commercial | Commercial Mortgage | Classified
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	19,754	21,460
Commercial | Construction
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	186,530	202,253
Commercial | Construction | Pass
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	183,240	198,926
Commercial | Construction | Special Mention
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	0	6
Commercial | Construction | Classified
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	3,290	3,321
Commercial | Lease Financing
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	179,771	180,931
Commercial | Lease Financing | Pass
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	179,401	180,522
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	10	11
Commercial | Lease Financing | Classified
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	360	398
Consumer
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	6,123,892	6,030,449	$ 5,483,314
Consumer | Pass
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	$ 6,111,511	6,015,043
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	$ 12,381	15,406
Consumer | Residential Mortgage
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	3,505,239	3,466,773
Consumer | Residential Mortgage | Pass
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	3,498,291	3,457,531
Consumer | Residential Mortgage | Classified
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	6,948	9,242
Consumer | Home Equity
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	1,601,698	1,585,455
Consumer | Home Equity | Pass
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	1,597,383	1,580,917
Consumer | Home Equity | Classified
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	4,315	4,538
Consumer | Automobile
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	558,468	528,474
Consumer | Automobile | Pass
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	558,135	527,587
Consumer | Automobile | Classified
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	333	887
Consumer | Other
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	458,487	449,747
Consumer | Other | Pass
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	457,702	449,008
Consumer | Other | Classified
Recorded Investment in Loans and Leases by Class and by Credit Quality Indicator
Total Recorded Investment in Loans and Leases	$ 785	$ 739