Allowance for Loan Losses Allowance by impairment analysis method (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	$ 981		$ 1,135
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	74,028		76,942
Loans and Leases Receivable, Allowance	75,009	$ 78,031	78,077	$ 75,753	$ 76,427	$ 78,500
Financing Receivable, Individually Evaluated for Impairment	24,017		26,030
Financing Receivable, Collectively Evaluated for Impairment	6,255,911		6,088,324
Total loans	6,279,928		6,114,354
Commercial and Industrial Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	11,672		12,751
Loans and Leases Receivable, Allowance	11,672	12,291	12,751	13,246	14,343	15,814
Financing Receivable, Individually Evaluated for Impairment	1,771		1,793
Financing Receivable, Collectively Evaluated for Impairment	956,142		1,008,181
Total loans	957,913		1,009,974
Commercial real estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	453		548
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	47,683		49,864
Loans and Leases Receivable, Allowance	48,136	51,164	50,412	45,507	44,519	44,215
Financing Receivable, Individually Evaluated for Impairment	9,875		11,603
Financing Receivable, Collectively Evaluated for Impairment	2,346,470		2,290,641
Total loans	2,356,345		2,302,244
Construction and land [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3,585		3,039
Loans and Leases Receivable, Allowance	3,585	3,197	3,039	4,740	5,551	6,322
Financing Receivable, Individually Evaluated for Impairment	232		179
Financing Receivable, Collectively Evaluated for Impairment	130,672		104,660
Total loans	130,904		104,839
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	507		565
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	9,775		9,884
Loans and Leases Receivable, Allowance	10,282	10,090	10,449	10,752	10,634	10,544
Financing Receivable, Individually Evaluated for Impairment	12,103		12,418
Financing Receivable, Collectively Evaluated for Impairment	2,513,122		2,367,443
Total loans	2,525,225		2,379,861
Home equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	21		22
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	908		1,013
Loans and Leases Receivable, Allowance	929	987	1,035	1,139	1,079	1,085
Financing Receivable, Individually Evaluated for Impairment	36		37
Financing Receivable, Collectively Evaluated for Impairment	108,513		118,780
Total loans	108,549		118,817
Consumer and other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	405		391
Loans and Leases Receivable, Allowance	405	$ 302	391	$ 369	$ 301	$ 520
Financing Receivable, Individually Evaluated for Impairment	0		0
Financing Receivable, Collectively Evaluated for Impairment	200,992		198,619
Total loans	$ 200,992		$ 198,619