Allowance for Loan Losses Allowance by impairment analysis method (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	$ 74,454	$ 74,393
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2,151	1,978
Loans and Leases Receivable, Allowance	76,605	76,371	82,286	84,057
Financing Receivable, Collectively Evaluated for Impairment	5,100,780	5,048,392
Financing Receivable, Individually Evaluated for Impairment	61,690	64,067
Total loans	5,162,470	5,112,459
Commercial and industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	12,126	12,737
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	74	100
Loans and Leases Receivable, Allowance	12,200	12,837	11,849	11,825
Financing Receivable, Collectively Evaluated for Impairment	849,070	862,616
Financing Receivable, Individually Evaluated for Impairment	3,131	3,437
Total loans	852,201	866,053
Commercial real estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	45,271	44,249
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,095	730
Loans and Leases Receivable, Allowance	46,366	44,979	50,466	52,497
Financing Receivable, Collectively Evaluated for Impairment	1,821,474	1,772,785
Financing Receivable, Individually Evaluated for Impairment	37,160	40,609
Total loans	1,858,634	1,813,394
Construction and land [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	4,733	4,229
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	239	236
Loans and Leases Receivable, Allowance	4,972	4,465	4,787	5,016
Financing Receivable, Collectively Evaluated for Impairment	171,262	150,087
Financing Receivable, Individually Evaluated for Impairment	3,454	3,830
Total loans	174,716	153,917
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	9,003	9,820
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	743	912
Loans and Leases Receivable, Allowance	9,746	10,732	11,454	10,892
Financing Receivable, Collectively Evaluated for Impairment	2,017,967	2,016,160
Financing Receivable, Individually Evaluated for Impairment	17,888	16,134
Total loans	2,035,855	2,032,294
Home equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	963	1,020
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0	0
Loans and Leases Receivable, Allowance	963	1,020	1,146	1,085
Financing Receivable, Collectively Evaluated for Impairment	108,913	113,610
Financing Receivable, Individually Evaluated for Impairment	50	50
Total loans	108,963	113,660
Consumer and other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	330	322
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0	0
Loans and Leases Receivable, Allowance	330	322	464	540
Financing Receivable, Collectively Evaluated for Impairment	132,094	133,134
Financing Receivable, Individually Evaluated for Impairment	7	7
Total loans	132,101	133,141
Unallocated Financing Receivables [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,028	2,016
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0	0
Loans and Leases Receivable, Allowance	2,028	2,016	2,120	2,202
Financing Receivable, Collectively Evaluated for Impairment	0	0
Financing Receivable, Individually Evaluated for Impairment	0	0
Total loans	$ 0	$ 0