Loans, Allowance for Loan Losses and Credit Quality (Allowance Allocations) (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment		$ 6,453,703	$ 6,269,729
Ending Balance: Individually Evaluated for Impairment		64,031	72,801
Financing Receivable, Net		4,637,962	4,539,256
Ending Balance: Total Loans by Group	[1]	6,527,402	6,355,553
Financial Asset Acquired with Credit Deterioration [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net		9,668	13,023
Commercial and Industrial [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment		972,842	853,885
Ending Balance: Individually Evaluated for Impairment		30,938	34,643
Financing Receivable, Net		1,003,780	888,528
Ending Balance: Total Loans by Group	[1]	1,003,780	888,528
Commercial and Industrial [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net		0	0
Commercial Real Estate [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment		3,114,414	3,093,945
Ending Balance: Individually Evaluated for Impairment		13,023	16,638
Financing Receivable, Net		3,132,491	3,116,561
Ending Balance: Total Loans by Group	[1]	3,132,491	3,116,561
Commercial Real Estate [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net		5,054	5,978
Construction Loans [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment		352,491	401,797
Ending Balance: Individually Evaluated for Impairment		0	0
Financing Receivable, Net		352,491	401,797
Ending Balance: Total Loans by Group	[1]	352,491	401,797
Construction Loans [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net		0	0
Small Business [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment		148,609	131,667
Ending Balance: Individually Evaluated for Impairment		591	703
Financing Receivable, Net		149,200	132,370
Ending Balance: Total Loans by Group	[1]	149,200	132,370
Small Business [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net		0	0
Residential Real Estate [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment		784,533	733,809
Ending Balance: Individually Evaluated for Impairment		12,825	13,684
Ending Balance: Total Loans by Group	[1]	801,810	754,329
Residential Real Estate [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net		4,452	6,836
Consumer Home Equity [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment		1,067,389	1,045,053
Ending Balance: Individually Evaluated for Impairment		6,410	6,826
Ending Balance: Total Loans by Group	[1]	1,073,961	1,052,088
Consumer Home Equity [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net		162	209
Consumer Other [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment		13,425	9,573
Ending Balance: Individually Evaluated for Impairment		244	307
Ending Balance: Total Loans by Group	[1]	13,669	9,880	[2]
Consumer Other [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net		$ 0	$ 0

[1] The amount of net deferred costs on originated loans included in the ending balance was $6.9 million and $6.1 million at September 30, 2018 and December 31, 2017, respectively. Net unamortized discounts on acquired loans not deemed to be purchased credit impaired ("PCI") included in the ending balance was $8.6 million and $9.4 million at September 30, 2018 and December 31, 2017, respectively.

[2] (1) Other consumer portfolio is inclusive of deposit account overdrafts recorded as loan balances.