Allowance for Loan Losses Allowance by impairment analysis method (Details) - USD ($)		Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		$ 1,316,000		$ 1,629,000
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		76,353,000		76,871,000
Loans and Leases Receivable, Allowance		77,669,000	$ 75,753,000	78,500,000	$ 79,246,000	$ 78,251,000	$ 75,838,000
Financing Receivable, Individually Evaluated for Impairment		38,482,000		39,172,000
Financing Receivable, Collectively Evaluated for Impairment		5,831,016,000		5,680,040,000
Total loans		5,869,498,000		5,719,212,000
Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans		0		0
Commercial and industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		22,000		270,000
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		13,879,000		15,544,000
Loans and Leases Receivable, Allowance		13,901,000	13,246,000	15,814,000	14,018,000	14,621,000	14,114,000
Financing Receivable, Individually Evaluated for Impairment		11,779,000		2,274,000
Financing Receivable, Collectively Evaluated for Impairment		1,087,391,000		1,109,281,000
Total loans		1,099,170,000		1,111,555,000
Commercial real estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		593,000		713,000
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		47,719,000		43,502,000
Loans and Leases Receivable, Allowance		48,312,000	45,507,000	44,215,000	45,124,000	44,133,000	43,854,000
Financing Receivable, Individually Evaluated for Impairment		13,130,000		19,462,000
Financing Receivable, Collectively Evaluated for Impairment		2,041,440,000		1,894,672,000
Total loans		2,054,570,000		1,914,134,000
Construction and land [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		0		172,000
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		3,144,000		6,150,000
Loans and Leases Receivable, Allowance		3,144,000	4,740,000	6,322,000	6,082,000	5,418,000	4,041,000
Financing Receivable, Individually Evaluated for Impairment		224,000		3,297,000
Financing Receivable, Collectively Evaluated for Impairment		98,472,000		180,137,000
Total loans		98,696,000		183,434,000
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		701,000		474,000
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		10,203,000		10,070,000
Loans and Leases Receivable, Allowance		10,904,000	10,752,000	10,544,000	10,529,000	10,394,000	10,374,000
Financing Receivable, Individually Evaluated for Impairment		13,349,000		14,139,000
Financing Receivable, Collectively Evaluated for Impairment		2,302,741,000		2,215,401,000
Total loans		2,316,090,000		2,229,540,000
Home equity [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		1,077,000		1,085,000
Loans and Leases Receivable, Allowance		1,077,000	1,139,000	1,085,000	979,000	1,024,000	1,003,000
Financing Receivable, Individually Evaluated for Impairment		0		0
Financing Receivable, Collectively Evaluated for Impairment		121,269,000		119,828,000
Total loans		121,269,000		119,828,000
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		331,000		520,000
Loans and Leases Receivable, Allowance		331,000	369,000	520,000	518,000	528,000	382,000
Financing Receivable, Individually Evaluated for Impairment		0		0
Financing Receivable, Collectively Evaluated for Impairment		179,703,000		160,721,000
Total loans		179,703,000		160,721,000
Unallocated Financing Receivables [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance	[1]	$ 0	$ 0	$ 0	$ 1,996,000	$ 2,133,000	$ 2,070,000

[1] As of December 31, 2015, the unallocated reserve was allocated to the qualitative factors as part of the general reserves (ASC 450).