Loan Portfolio and Credit Quality Impaired Loans With and Without Related Allowance (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	[1]	$ 12,900	$ 24,404	$ 12,900	$ 24,404	$ 14,594
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	8,745	14,078	8,745	14,078	11,436
Impaired Financing Receivable, Recorded Investment	[1]	21,645	38,482	21,645	38,482	26,030
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		17,432	32,402	17,432	32,402	20,815
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		9,175	14,507	9,175	14,507	11,865
Impaired Financing Receivable, Unpaid Principal Balance		26,607	46,909	26,607	46,909	32,680
Impaired Financing Receivable, Related Allowance		805	1,316	805	1,316	1,135
Impaired Financing Receivable, Related Allowance		805	1,316	805	1,316	1,135
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		13,603	25,807	15,560	24,674	22,323
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		9,315	13,208	10,047	13,946	13,276
Impaired Financing Receivable, Average Recorded Investment		22,918	39,015	25,607	38,620	35,599
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method		223	537	1,477	1,264	1,540
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		95	115	329	353	458
Impaired Financing Receivable, Interest Income, Cash Basis Method		318	652	1,806	1,617	1,998
Commercial and industrial [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	[1]	1,371	11,742	1,371	11,742	1,793
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	598	37	598	37	0
Impaired Financing Receivable, Recorded Investment	[1]	1,969	11,779	1,969	11,779	1,793
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		1,988	13,874	1,988	13,874	2,155
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		598	37	598	37	0
Impaired Financing Receivable, Unpaid Principal Balance		2,586	13,911	2,586	13,911	2,155
Impaired Financing Receivable, Related Allowance		242	22	242	22	0
Impaired Financing Receivable, Related Allowance		242	22	242	22	0
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		1,626	10,774	1,665	6,325	5,288
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		149	37	60	33	31
Impaired Financing Receivable, Average Recorded Investment		1,775	10,811	1,725	6,358	5,319
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method		18	98	43	169	249
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		1	0	1	1	1
Impaired Financing Receivable, Interest Income, Cash Basis Method		19	98	44	170	250
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	0	1,301	0	0
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		0	0	0	0	0
Impaired Financing Receivable, Average Recorded Investment		0	0	1,301	0	0
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method		0	0	80	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		0	0	80	0	0
Commercial real estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	[1]	2,463	5,966	2,463	5,966	4,488
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	6,911	7,164	6,911	7,164	7,115
Impaired Financing Receivable, Recorded Investment	[1]	9,374	13,130	9,374	13,130	11,603
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		5,972	11,148	5,972	11,148	9,647
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		7,341	7,593	7,341	7,593	7,544
Impaired Financing Receivable, Unpaid Principal Balance		13,313	18,741	13,313	18,741	17,191
Impaired Financing Receivable, Related Allowance		415	593	415	593	548
Impaired Financing Receivable, Related Allowance		415	593	415	593	548
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		2,690	7,288	3,465	9,672	8,520
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		6,955	7,194	7,012	7,259	7,230
Impaired Financing Receivable, Average Recorded Investment		9,645	14,482	10,477	16,931	15,750
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method		107	332	1,077	874	1,032
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		76	79	247	237	314
Impaired Financing Receivable, Interest Income, Cash Basis Method		183	411	1,324	1,111	1,346
Construction and land [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	[1]	207	224	207	224	179
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	0	0	0	0	0
Impaired Financing Receivable, Recorded Investment	[1]	207	224	207	224	179
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		241	548	241	548	507
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		0	0	0	0	0
Impaired Financing Receivable, Unpaid Principal Balance		241	548	241	548	507
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		218	400	191	1,332	1,069
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		0	0	0	660	507
Impaired Financing Receivable, Average Recorded Investment		218	400	191	1,992	1,576
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method		0	48	0	48	48
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	48	0	48	48
Residential [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	[1]	8,859	6,472	8,859	6,472	8,134
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	1,200	6,877	1,200	6,877	4,284
Impaired Financing Receivable, Recorded Investment	[1]	10,059	13,349	10,059	13,349	12,418
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		9,231	6,832	9,231	6,832	8,506
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		1,200	6,877	1,200	6,877	4,284
Impaired Financing Receivable, Unpaid Principal Balance		10,431	13,709	10,431	13,709	12,790
Impaired Financing Receivable, Related Allowance		127	701	127	701	565
Impaired Financing Receivable, Related Allowance		127	701	127	701	565
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		9,069	7,345	8,938	7,345	7,446
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		2,175	5,977	2,938	5,994	5,505
Impaired Financing Receivable, Average Recorded Investment		11,244	13,322	11,876	13,339	12,951
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method		98	59	277	173	211
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method		18	36	80	115	143
Impaired Financing Receivable, Interest Income, Cash Basis Method		116	95	357	288	354
Home equity [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]	36	0	36	0	37
Impaired Financing Receivable, Recorded Investment	[1]	36	0	36	0	37
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance		0	0	0	0	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		36	0	36	0	37
Impaired Financing Receivable, Unpaid Principal Balance		36	0	36	0	37
Impaired Financing Receivable, Related Allowance		21	0	21	0	22
Impaired Financing Receivable, Related Allowance		21	0	21	0	22
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		0	0	0	0	0
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		36	0	37	0	3
Impaired Financing Receivable, Average Recorded Investment		36	0	37	0	3
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	1	0	0
Impaired Financing Receivable, Interest Income, Cash Basis Method		0	0	1	0	0
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	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	0	0	0	0
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		0	0	0	0	0
Impaired Financing Receivable, Average Recorded Investment		0	0	0	0	0
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	0	0	0
Impaired Financing Receivable, Interest Income, Cash Basis Method		$ 0	$ 0	$ 0	$ 0	$ 0

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