Allowance for Loan Losses Allowance Rollforward (Details) - USD ($) $ in Thousands		3 Months Ended																12 Months Ended
		Dec. 31, 2017		Sep. 30, 2017	[1]	Jun. 30, 2017	[1]	Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Beginning of Period								$ 78,077								$ 78,500		$ 78,077	$ 78,500	$ 75,838
Provision/ (credit) for loan losses		$ (942)	[1]	$ (432)		$ (6,114)		(181)	[1]	$ (1,128)	[1]	$ (138)		$ (2,535)		(3,133)	[1]	(7,669)	(6,935)	(1,555)
Loans charged-off																		(863)	(3,949)	(2,036)
Financing Receivable, Allowance for Credit Losses, Recovery																		5,197	10,461	6,253
Loans and Leases Receivable, Allowance, End of Period		74,742								78,077								74,742	78,077	78,500
Commercial and Industrial Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Beginning of Period																15,814			15,814	14,114
Provision/ (credit) for loan losses																				(518)
Loans charged-off																				(253)
Financing Receivable, Allowance for Credit Losses, Recovery																				2,471
Loans and Leases Receivable, Allowance, End of Period																				15,814
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Beginning of Period																44,215			44,215	43,854
Provision/ (credit) for loan losses																				(721)
Loans charged-off																				(1,400)
Financing Receivable, Allowance for Credit Losses, Recovery																				2,482
Loans and Leases Receivable, Allowance, End of Period																				44,215
Construction Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Beginning of Period																6,322			6,322	4,041
Provision/ (credit) for loan losses																				1,123
Loans charged-off																				0
Financing Receivable, Allowance for Credit Losses, Recovery																				1,158
Loans and Leases Receivable, Allowance, End of Period																				6,322
Residential Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Beginning of Period																10,544			10,544	10,374
Provision/ (credit) for loan losses																				342
Loans charged-off																				(313)
Financing Receivable, Allowance for Credit Losses, Recovery																				141
Loans and Leases Receivable, Allowance, End of Period																				10,544
Home Equity Line of Credit [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Beginning of Period																1,085			1,085	1,003
Provision/ (credit) for loan losses																				82
Loans charged-off																				0
Financing Receivable, Allowance for Credit Losses, Recovery																				0
Loans and Leases Receivable, Allowance, End of Period																				1,085
Consumer Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Beginning of Period																520			520	382
Provision/ (credit) for loan losses																				207
Loans charged-off																				(70)
Financing Receivable, Allowance for Credit Losses, Recovery																				1
Loans and Leases Receivable, Allowance, End of Period																				520
Unallocated Financing Receivables [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Beginning of Period	[2]							0								0		0	0	2,070
Provision/ (credit) for loan losses	[2]																	0	0	(2,070)
Loans and Leases Receivable, Allowance, End of Period	[2]									0									0	0
Consumer Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Beginning of Period								391								520		391	520
Provision/ (credit) for loan losses																		619	(63)
Loans charged-off																		(412)	(93)
Financing Receivable, Allowance for Credit Losses, Recovery																		32	27
Loans and Leases Receivable, Allowance, End of Period		630								391								630	391	520
Home Equity Line of Credit [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Beginning of Period								1,035								1,085		1,035	1,085
Provision/ (credit) for loan losses																		(200)	(50)
Loans charged-off																		0	0
Financing Receivable, Allowance for Credit Losses, Recovery																		0	0
Loans and Leases Receivable, Allowance, End of Period		835								1,035								835	1,035	1,085
Residential Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Beginning of Period								10,449								10,544		10,449	10,544
Provision/ (credit) for loan losses																		(665)	445
Loans charged-off																		(58)	(605)
Financing Receivable, Allowance for Credit Losses, Recovery																		47	65
Loans and Leases Receivable, Allowance, End of Period		9,773								10,449								9,773	10,449	10,544
Construction Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Beginning of Period								3,039								6,322		3,039	6,322
Provision/ (credit) for loan losses																		1,885	(4,000)
Loans charged-off																		0	(400)
Financing Receivable, Allowance for Credit Losses, Recovery																		25	1,117
Loans and Leases Receivable, Allowance, End of Period		4,949								3,039								4,949	3,039	6,322
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Beginning of Period								50,412								44,215		50,412	44,215
Provision/ (credit) for loan losses																		(8,213)	157
Loans charged-off																		0	0
Financing Receivable, Allowance for Credit Losses, Recovery																		4,621	6,040
Loans and Leases Receivable, Allowance, End of Period		46,820								50,412								46,820	50,412	44,215
Commercial and Industrial Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Beginning of Period								$ 12,751								$ 15,814		12,751	15,814
Provision/ (credit) for loan losses																		(1,095)	(3,424)
Loans charged-off																		(393)	(2,851)
Financing Receivable, Allowance for Credit Losses, Recovery																		472	3,212
Loans and Leases Receivable, Allowance, End of Period		$ 11,735								$ 12,751								$ 11,735	$ 12,751	$ 15,814

[1] Due to rounding, the sum of the four quarters may not add to the year to date total.

[2] As of December 31, 2015, the unallocated reserve was allocated to the qualitative factors as part of the general reserve (ASC 450). The allocation had no effect on the 2015 provision/ (credit) for loan losses.