Loans, Allowance for Loan Losses and Credit Quality (Allowance Allocations) (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment		$ 6,279,723	$ 6,269,729
Ending Balance: Individually Evaluated for Impairment		70,923	72,801
Financing Receivable, Net		4,540,085	4,539,256
Ending Balance: Total Loans by Group	[1]	6,362,056	6,355,553
Receivables Acquired with Deteriorated Credit Quality [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net		11,410	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		870,110	853,885
Ending Balance: Individually Evaluated for Impairment		33,104	34,643
Financing Receivable, Net		903,214	888,528
Ending Balance: Total Loans by Group	[1]	903,214	888,528
Commercial and Industrial [Member] | Receivables Acquired with Deteriorated Credit Quality [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		3,079,910	3,093,945
Ending Balance: Individually Evaluated for Impairment		16,470	16,638
Financing Receivable, Net		3,102,271	3,116,561
Ending Balance: Total Loans by Group	[1]	3,102,271	3,116,561
Commercial Real Estate [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net		5,891	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		400,934	401,797
Ending Balance: Individually Evaluated for Impairment		0	0
Financing Receivable, Net		400,934	401,797
Ending Balance: Total Loans by Group	[1]	400,934	401,797
Construction Loans [Member] | Receivables Acquired with Deteriorated Credit Quality [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		132,813	131,667
Ending Balance: Individually Evaluated for Impairment		853	703
Financing Receivable, Net		133,666	132,370
Ending Balance: Total Loans by Group	[1]	133,666	132,370
Small Business [Member] | Receivables Acquired with Deteriorated Credit Quality [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		742,744	733,809
Ending Balance: Individually Evaluated for Impairment		13,278	13,684
Ending Balance: Total Loans by Group	[1]	761,331	754,329
Residential Real Estate [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net		5,309	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		1,044,316	1,045,053
Ending Balance: Individually Evaluated for Impairment		6,926	6,826
Ending Balance: Total Loans by Group	[1]	1,051,452	1,052,088
Consumer Home Equity [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net		210	209
Consumer Other [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment		8,896	9,573
Ending Balance: Individually Evaluated for Impairment		292	307
Ending Balance: Total Loans by Group	[1]	9,188	9,880	[2]
Consumer Other [Member] | Receivables Acquired with Deteriorated Credit Quality [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 $6.4 million and $6.1 million at March 31, 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 $9.1 million and $9.4 million at March 31, 2018 and December 31, 2017, respectively.

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