Allowance for Loan Losses Allowance by impairment analysis method (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	$ 93,185		$ 91,906
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	5,869		4,208
Loans and Leases Receivable, Allowance	99,054	97,902	96,114	98,742	100,282	98,403
Financing Receivable, Collectively Evaluated for Impairment	5,002,998		4,561,435
Financing Receivable, Individually Evaluated for Impairment	88,130		89,793
Total loans	5,091,128		4,651,228
Commercial and industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	12,230		12,014
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,013		149
Loans and Leases Receivable, Allowance	13,243	12,062	12,163	12,460	13,864	13,438
Financing Receivable, Collectively Evaluated for Impairment	811,797		680,384
Financing Receivable, Individually Evaluated for Impairment	6,573		6,718
Total loans	818,370		687,102
Commercial real estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	62,165		60,318
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2,412		3,307
Loans and Leases Receivable, Allowance	64,577	65,366	63,625	66,914	68,293	65,760
Financing Receivable, Collectively Evaluated for Impairment	1,773,791		1,611,055
Financing Receivable, Individually Evaluated for Impairment	49,782		58,165
Total loans	1,823,573		1,669,220
Construction and land [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	4,986		6,163
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,177		219
Loans and Leases Receivable, Allowance	6,163	5,836	6,382	6,004	5,887	6,875
Financing Receivable, Collectively Evaluated for Impairment	155,489		145,937
Financing Receivable, Individually Evaluated for Impairment	8,633		7,772
Total loans	164,122		153,709
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	9,708		8,884
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,136		402
Loans and Leases Receivable, Allowance	10,844	10,054	9,286	8,499	7,873	7,449
Financing Receivable, Collectively Evaluated for Impairment	1,969,134		1,806,722
Financing Receivable, Individually Evaluated for Impairment	22,553		16,681
Total loans	1,991,687		1,823,403
Home equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,358		1,404
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	131		131
Loans and Leases Receivable, Allowance	1,489	1,543	1,535	1,291	1,199	1,231
Financing Receivable, Collectively Evaluated for Impairment	136,067		143,241
Financing Receivable, Individually Evaluated for Impairment	491		457
Total loans	136,558		143,698
Consumer and other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	740		1,149
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Loans and Leases Receivable, Allowance	740	1,009	1,149	1,616	1,463	1,478
Financing Receivable, Collectively Evaluated for Impairment	156,720		174,096
Financing Receivable, Individually Evaluated for Impairment	98		0
Total loans	156,818		174,096
Unallocated Financing Receivables [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,998		1,974
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Loans and Leases Receivable, Allowance	1,998	2,032	1,974	1,958	1,703	2,172
Financing Receivable, Collectively Evaluated for Impairment	0		0
Financing Receivable, Individually Evaluated for Impairment	0		0
Total loans	$ 0		$ 0