Loans, Allowance for Loan Losses and Credit Quality (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	$ 4,056,135	[1]	$ 3,794,390	[1]
Ending Balance: Individually Evaluated for Impairment	69,590		61,701
Ending Balance: Collectively Evaluated for Impairment	3,986,545		3,732,689
Commercial and Industrial [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	653,861		575,716
Ending Balance: Individually Evaluated for Impairment	8,451		5,608
Ending Balance: Collectively Evaluated for Impairment	645,410		570,108
Commercial Real Estate [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	1,939,245		1,847,654
Ending Balance: Individually Evaluated for Impairment	35,653		37,476
Ending Balance: Collectively Evaluated for Impairment	1,903,592		1,810,178
Commercial Construction [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	175,731		128,904
Ending Balance: Individually Evaluated for Impairment	0		843
Ending Balance: Collectively Evaluated for Impairment	175,731		128,061
Small Business [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	78,794		78,509
Ending Balance: Individually Evaluated for Impairment	2,636		2,326
Ending Balance: Collectively Evaluated for Impairment	76,158		76,183
Residential Real Estate [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	384,948		426,201
Ending Balance: Individually Evaluated for Impairment	16,273		12,984
Ending Balance: Collectively Evaluated for Impairment	368,675		413,217
Consumer Home Equity [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	794,375		696,063
Ending Balance: Individually Evaluated for Impairment	4,284		326
Ending Balance: Collectively Evaluated for Impairment	790,091		695,737
Consumer Other [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Total Loans by Group	29,181		41,343
Ending Balance: Individually Evaluated for Impairment	2,293		2,138
Ending Balance: Collectively Evaluated for Impairment	$ 26,888		$ 39,205

[1] The amount of deferred fees included in the ending balance was $3.2 million and $2.9 million at September 30, 2012 and December 31, 2011, respectively.