Loans Receivable and Credit Quality Loans by Grade or Nonaccrual Status (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 4,967,607	$ 4,651,228
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,691,985	4,341,757
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	94,422	143,121
Accruing Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	107,806	98,241
Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	73,394	68,109
Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	786,335	678,048
Commercial and industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	756,475	641,831
Commercial and industrial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,095	10,209
Commercial and industrial [Member] | Accruing Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,370	22,249
Commercial and industrial [Member] | Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,395	3,759
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,804,811	1,678,274
Commercial real estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,608,853	1,454,786
Commercial real estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	70,914	121,802
Commercial real estate [Member] | Accruing Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	83,771	63,105
Commercial real estate [Member] | Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	41,273	38,581
Construction and land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	164,891	153,709
Construction and land [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	146,804	131,205
Construction and land [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,321	10,978
Construction and land [Member] | Accruing Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,118	3,754
Construction and land [Member] | Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,648	7,772
Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,941,217	1,823,403
Residential [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,914,346	1,798,635
Residential [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Residential [Member] | Accruing Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,679	7,255
Residential [Member] | Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	19,192	17,513
Home equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	128,252	143,698
Home equity [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	125,594	141,373
Home equity [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Home equity [Member] | Accruing Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,868	1,868
Home equity [Member] | Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	790	457
Consumer and other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	142,101	174,096
Consumer and other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	139,913	173,927
Consumer and other [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,092	132
Consumer and other [Member] | Accruing Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	10
Consumer and other [Member] | Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 96	$ 27