Loans, Allowance for Loan Losses and Credit Quality (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	$ 4,487,478	[1]	$ 4,519,011	[1]
Ending Balance: Individually Evaluated for Impairment	65,495		66,659
Financing Receivable, Acquired with Deteriorated Credit Quality	30,022		32,054
Ending Balance: Collectively Evaluated for Impairment	4,391,961		4,420,298
Commercial and Industrial [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	702,486		687,511
Ending Balance: Individually Evaluated for Impairment	7,773		8,575
Financing Receivable, Acquired with Deteriorated Credit Quality	0		0
Ending Balance: Collectively Evaluated for Impairment	694,713		678,936
Commercial Real Estate [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	2,123,778		2,122,153
Ending Balance: Individually Evaluated for Impairment	31,285		33,868
Financing Receivable, Acquired with Deteriorated Credit Quality	20,138		21,853
Ending Balance: Collectively Evaluated for Impairment	2,072,355		2,066,432
Commercial Construction [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	211,984		188,768
Ending Balance: Individually Evaluated for Impairment	1,608		0
Financing Receivable, Acquired with Deteriorated Credit Quality	0		0
Ending Balance: Collectively Evaluated for Impairment	210,376		188,768
Small Business [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	77,220		78,594
Ending Balance: Individually Evaluated for Impairment	2,073		2,279
Financing Receivable, Acquired with Deteriorated Credit Quality	0		0
Ending Balance: Collectively Evaluated for Impairment	75,147		76,315
Residential Real Estate [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	555,413		612,881
Ending Balance: Individually Evaluated for Impairment	16,428		15,373
Financing Receivable, Acquired with Deteriorated Credit Quality	9,509		9,821
Ending Balance: Collectively Evaluated for Impairment	529,476		587,687
Consumer Home Equity [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	792,630		802,149
Ending Balance: Individually Evaluated for Impairment	4,446		4,435
Financing Receivable, Acquired with Deteriorated Credit Quality	375		380
Ending Balance: Collectively Evaluated for Impairment	787,809		797,334
Consumer Other [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	23,967		26,955
Ending Balance: Individually Evaluated for Impairment	1,882		2,129
Financing Receivable, Acquired with Deteriorated Credit Quality	0		0
Ending Balance: Collectively Evaluated for Impairment	$ 22,085		$ 24,826

[1] The amount of deferred fees included in the ending balance was $2.9 million and $3.1 million at March 31, 2013 and December 31, 2012, respectively.