Loan Portfolio and Credit Quality Impaired Loans With and Without Related Allowance (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	[1]	$ 15,402	$ 14,482	$ 15,402	$ 14,482	$ 14,491
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	8,314	9,535	8,314	9,535	8,086
Impaired Financing Receivable, Recorded Investment	[1]	23,716	24,017	23,716	24,017	22,577
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		18,464	19,345	18,464	19,345	17,288
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		8,843	9,964	8,843	9,964	8,640
Impaired Financing Receivable, Unpaid Principal Balance		27,307	29,309	27,307	29,309	25,928
Impaired Financing Receivable, Related Allowance		1,000	981	1,000	981	654
Impaired Financing Receivable, Related Allowance		1,000	981	1,000	981	654
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		16,967	15,860	15,907	16,525	15,311
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		6,830	9,661	7,325	10,391	9,651
Impaired Financing Receivable, Average Recorded Investment		23,797	25,521	23,232	26,916	24,962
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method		157	894	301	1,254	2,036
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		78	119	245	233	416
Impaired Financing Receivable, Interest Income, Cash Basis Method		235	1,013	546	1,487	2,452
Commercial and industrial [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	[1]	2,015	1,771	2,015	1,771	1,434
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	303	0	303	0	242
Impaired Financing Receivable, Recorded Investment	[1]	2,318	1,771	2,318	1,771	1,676
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		2,954	2,377	2,954	2,377	2,238
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		403	0	403	0	242
Impaired Financing Receivable, Unpaid Principal Balance		3,357	2,377	3,357	2,377	2,480
Impaired Financing Receivable, Related Allowance		134	0	134	0	58
Impaired Financing Receivable, Related Allowance		134	0	134	0	58
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		2,048	1,667	1,835	1,703	1,594
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		76	0	147	0	156
Impaired Financing Receivable, Average Recorded Investment		2,124	1,667	1,982	1,703	1,750
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method		14	12	22	25	50
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		0	0	2	0	4
Impaired Financing Receivable, Interest Income, Cash Basis Method		14	12	24	25	54
Commercial Tax Exempt [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	[1]	0	0	0	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	0	0	0	0	0
Impaired Financing Receivable, Recorded Investment	[1]	0	0	0	0	0
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		0	0	0	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		0	0	0	0	0
Impaired Financing Receivable, Unpaid Principal Balance		0	0	0	0	0
Impaired Financing Receivable, Related Allowance		0	0	0	0	0
Impaired Financing Receivable, Related Allowance		0	0	0	0	0
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		0	1,084	0	1,859	1,001
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		0	0	0	0	0
Impaired Financing Receivable, Average Recorded Investment		0	1,084	0	1,859	1,001
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method		0	80	0	80	80
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		0	0	0	0	0
Impaired Financing Receivable, Interest Income, Cash Basis Method		0	80	0	80	80
Commercial real estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	[1]	2,932	2,879	2,932	2,879	1,832
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	5,426	6,996	5,426	6,996	6,855
Impaired Financing Receivable, Recorded Investment	[1]	8,358	9,875	8,358	9,875	8,687
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		4,695	6,429	4,695	6,429	3,453
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		5,855	7,425	5,855	7,425	7,284
Impaired Financing Receivable, Unpaid Principal Balance		10,550	13,854	10,550	13,854	10,737
Impaired Financing Receivable, Related Allowance		187	453	187	453	362
Impaired Financing Receivable, Related Allowance		187	453	187	453	362
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		2,939	3,358	2,460	3,824	3,098
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		5,467	7,011	6,055	7,042	6,980
Impaired Financing Receivable, Average Recorded Investment		8,406	10,369	8,515	10,866	10,078
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method		25	724	50	970	1,546
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		72	96	228	171	322
Impaired Financing Receivable, Interest Income, Cash Basis Method		97	820	278	1,141	1,868
Construction and land [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	[1]	0	232	0	232	109
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	0	0	0	0	0
Impaired Financing Receivable, Recorded Investment	[1]	0	232	0	232	109
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		0	568	0	568	109
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		0	0	0	0	0
Impaired Financing Receivable, Unpaid Principal Balance		0	568	0	568	109
Impaired Financing Receivable, Related Allowance		0	0	0	0	0
Impaired Financing Receivable, Related Allowance		0	0	0	0	0
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		82	190	94	181	172
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		0	0	0	0	0
Impaired Financing Receivable, Average Recorded Investment		82	190	94	181	172
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method		16	0	16	0	0
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		0	0	0	0	0
Impaired Financing Receivable, Interest Income, Cash Basis Method		16	0	16	0	0
Residential [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	[1]	10,455	9,600	10,455	9,600	9,337
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	816	2,503	816	2,503	828
Impaired Financing Receivable, Recorded Investment	[1]	11,271	12,103	11,271	12,103	10,165
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		10,815	9,971	10,815	9,971	9,709
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		816	2,503	816	2,503	828
Impaired Financing Receivable, Unpaid Principal Balance		11,631	12,474	11,631	12,474	10,537
Impaired Financing Receivable, Related Allowance		82	507	82	507	89
Impaired Financing Receivable, Related Allowance		82	507	82	507	89
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		10,587	9,561	10,009	8,958	9,033
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		818	2,613	821	3,312	2,469
Impaired Financing Receivable, Average Recorded Investment		11,405	12,174	10,830	12,270	11,502
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method		87	78	189	179	360
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		6	23	12	62	89
Impaired Financing Receivable, Interest Income, Cash Basis Method		93	101	201	241	449
Home equity [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	[1]	0	0	0	0	1,779
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	1,769	36	1,769	36	36
Impaired Financing Receivable, Recorded Investment	[1]	1,769	36	1,769	36	1,815
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		0	0	0	0	1,779
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		1,769	36	1,769	36	36
Impaired Financing Receivable, Unpaid Principal Balance		1,769	36	1,769	36	1,815
Impaired Financing Receivable, Related Allowance		597	21	597	21	20
Impaired Financing Receivable, Related Allowance		597	21	597	21	20
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		1,311	0	1,509	0	413
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		469	37	284	37	36
Impaired Financing Receivable, Average Recorded Investment		1,780	37	1,793	37	449
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method		15	0	24	0	0
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		0	0	0	0	1
Impaired Financing Receivable, Interest Income, Cash Basis Method		15	0	24	0	1
Consumer and other [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	[1]	0	0	0	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	0	0	0	0	125
Impaired Financing Receivable, Recorded Investment	[1]	0	0	0	0	125
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		0	0	0	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		0	0	0	0	250
Impaired Financing Receivable, Unpaid Principal Balance		0	0	0	0	250
Impaired Financing Receivable, Related Allowance		0	0	0	0	125
Impaired Financing Receivable, Related Allowance		0	0	0	0	125
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		0	0	0	0	0
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		0	0	18	0	10
Impaired Financing Receivable, Average Recorded Investment		0	0	18	0	10
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method		0	0	0	0	0
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		0	0	3	0	0
Impaired Financing Receivable, Interest Income, Cash Basis Method		$ 0	$ 0	$ 3	$ 0	$ 0

[1] Recorded investment represents the client loan balance net of historical charge-offs and historical nonaccrual interest paid, if applicable, which was applied to principal.