Allowance for Loan Losses Allowance by impairment analysis method (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Jun. 30, 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	$ 72,640		$ 74,393
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,907		1,978
Loans and Leases Receivable, Allowance	74,547	76,605	76,371	80,800	82,286	84,057
Financing Receivable, Collectively Evaluated for Impairment	5,047,419		5,048,392
Financing Receivable, Individually Evaluated for Impairment	58,632		64,067
Total loans	5,106,051		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	13,067		12,737
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	74		100
Loans and Leases Receivable, Allowance	13,141	12,200	12,837	11,883	11,849	11,825
Financing Receivable, Collectively Evaluated for Impairment	879,366		862,616
Financing Receivable, Individually Evaluated for Impairment	3,097		3,437
Total loans	882,463		866,053
Commercial real estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	43,083		44,249
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,003		730
Loans and Leases Receivable, Allowance	44,086	46,366	44,979	48,744	50,466	52,497
Financing Receivable, Collectively Evaluated for Impairment	1,749,030		1,772,785
Financing Receivable, Individually Evaluated for Impairment	31,871		40,609
Total loans	1,780,901		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	4,359		4,229
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	221		236
Loans and Leases Receivable, Allowance	4,580	4,972	4,465	4,923	4,787	5,016
Financing Receivable, Collectively Evaluated for Impairment	147,026		150,087
Financing Receivable, Individually Evaluated for Impairment	3,396		3,830
Total loans	150,422		153,917
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	8,960		9,820
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	609		912
Loans and Leases Receivable, Allowance	9,569	9,746	10,732	11,625	11,454	10,892
Financing Receivable, Collectively Evaluated for Impairment	2,019,861		2,016,160
Financing Receivable, Individually Evaluated for Impairment	19,211		16,134
Total loans	2,039,072		2,032,294
Home equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	992		1,020
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Loans and Leases Receivable, Allowance	992	963	1,020	1,201	1,146	1,085
Financing Receivable, Collectively Evaluated for Impairment	112,454		113,610
Financing Receivable, Individually Evaluated for Impairment	50		50
Total loans	112,504		113,660
Consumer and other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	257		322
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Loans and Leases Receivable, Allowance	257	330	322	412	464	540
Financing Receivable, Collectively Evaluated for Impairment	139,682		133,134
Financing Receivable, Individually Evaluated for Impairment	1,007		7
Total loans	140,689		133,141
Unallocated Financing Receivables [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,922		2,016
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Loans and Leases Receivable, Allowance	1,922	2,028	2,016	2,012	2,120	2,202
Financing Receivable, Collectively Evaluated for Impairment	0		0
Financing Receivable, Individually Evaluated for Impairment	0		0
Total loans	$ 0		$ 0