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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Recorded Investment
With no related allowance recorded:	$ 19,293	$ 15,402	$ 19,293	$ 15,402	$ 11,374
With an allowance recorded:	1,493	8,314	1,493	8,314	4,269
Total:	20,786	23,716	20,786	23,716	15,643
Unpaid Principal Balance
With no related allowance recorded:	21,062	18,464	21,062	18,464	13,051
With an allowance recorded:	1,493	8,843	1,493	8,843	4,471
Total:	22,555	27,307	22,555	27,307	17,522
Related Allowance	191	1,000	191	1,000	1,235
Average Recorded Investment
With no related allowance recorded:	17,958	16,967	16,029	15,907	14,345
With an allowance recorded:	1,398	6,830	2,564	7,325	6,472
Total:	19,356	23,797	18,593	23,232	20,817
Interest Income Recognized while Impaired
With no related allowance recorded:	114	157	522	301	2,061
With an allowance recorded:	11	78	34	245	756
Total:	125	235	556	546	2,817
Commercial and industrial
Recorded Investment
With no related allowance recorded:	1,669	2,015	1,669	2,015	1,435
With an allowance recorded:	441	303	441	303	1,770
Total:	2,110	2,318	2,110	2,318	3,205
Unpaid Principal Balance
With no related allowance recorded:	2,616	2,954	2,616	2,954	2,397
With an allowance recorded:	441	403	441	403	1,972
Total:	3,057	3,357	3,057	3,357	4,369
Related Allowance	93	134	93	134	598
Average Recorded Investment
With no related allowance recorded:	1,520	2,048	1,328	1,835	1,614
With an allowance recorded:	596	76	1,036	147	631
Total:	2,116	2,124	2,364	1,982	2,245
Interest Income Recognized while Impaired
With no related allowance recorded:	10	14	25	22	69
With an allowance recorded:	4	0	20	2	15
Total:	14	14	45	24	84
Commercial tax-exempt
Recorded Investment
With no related allowance recorded:	0	0	0	0	0
With an allowance recorded:	0	0	0	0	0
Total:	0	0	0	0	0
Unpaid Principal Balance
With no related allowance recorded:	0	0	0	0	0
With an allowance recorded:	0	0	0	0	0
Total:	0	0	0	0	0
Related Allowance	0	0	0	0	0
Average Recorded Investment
With no related allowance recorded:	0	0	0	0	0
With an allowance recorded:	0	0	0	0	0
Total:	0	0	0	0	0
Interest Income Recognized while Impaired
With no related allowance recorded:	0	0	0	0	0
With an allowance recorded:	0	0	0	0	0
Total:	0	0	0	0	0
Commercial real estate
Recorded Investment
With no related allowance recorded:	0	2,932	0	2,932	546
With an allowance recorded:	0	5,426	0	5,426	0
Total:	0	8,358	0	8,358	546
Unpaid Principal Balance
With no related allowance recorded:	0	4,695	0	4,695	900
With an allowance recorded:	0	5,855	0	5,855	0
Total:	0	10,550	0	10,550	900
Related Allowance	0	187	0	187	0
Average Recorded Investment
With no related allowance recorded:	0	2,939	78	2,460	2,002
With an allowance recorded:	0	5,467	0	6,055	4,087
Total:	0	8,406	78	8,515	6,089
Interest Income Recognized while Impaired
With no related allowance recorded:	0	25	256	50	1,544
With an allowance recorded:	0	72	0	228	705
Total:	0	97	256	278	2,249
Construction and land
Recorded Investment
With no related allowance recorded:	0	0	0	0	0
With an allowance recorded:	0	0	0	0	0
Total:	0	0	0	0	0
Unpaid Principal Balance
With no related allowance recorded:	0	0	0	0	0
With an allowance recorded:	0	0	0	0	0
Total:	0	0	0	0	0
Related Allowance	0	0	0	0	0
Average Recorded Investment
With no related allowance recorded:	0	82	0	94	50
With an allowance recorded:	0	0	0	0	0
Total:	0	82	0	94	50
Interest Income Recognized while Impaired
With no related allowance recorded:	0	16	0	16	16
With an allowance recorded:	0	0	0	0	0
Total:	0	16	0	16	16
Residential
Recorded Investment
With no related allowance recorded:	15,127	10,455	15,127	10,455	8,403
With an allowance recorded:	778	816	778	816	780
Total:	15,905	11,271	15,905	11,271	9,183
Unpaid Principal Balance
With no related allowance recorded:	15,387	10,815	15,387	10,815	8,764
With an allowance recorded:	778	816	778	816	780
Total:	16,165	11,631	16,165	11,631	9,544
Related Allowance	74	82	74	82	75
Average Recorded Investment
With no related allowance recorded:	14,079	10,587	12,605	10,009	9,638
With an allowance recorded:	733	818	752	821	785
Total:	14,812	11,405	13,357	10,830	10,423
Interest Income Recognized while Impaired
With no related allowance recorded:	103	87	240	189	408
With an allowance recorded:	6	6	13	12	22
Total:	109	93	253	201	430
Home equity
Recorded Investment
With no related allowance recorded:	2,497	0	2,497	0	990
With an allowance recorded:	274	1,769	274	1,769	1,719
Total:	2,771	1,769	2,771	1,769	2,709
Unpaid Principal Balance
With no related allowance recorded:	3,059	0	3,059	0	990
With an allowance recorded:	274	1,769	274	1,769	1,719
Total:	3,333	1,769	3,333	1,769	2,709
Related Allowance	24	597	24	597	562
Average Recorded Investment
With no related allowance recorded:	2,359	1,311	2,018	1,509	1,041
With an allowance recorded:	69	469	776	284	959
Total:	2,428	1,780	2,794	1,793	2,000
Interest Income Recognized while Impaired
With no related allowance recorded:	1	15	1	24	24
With an allowance recorded:	1	0	1	0	11
Total:	2	15	2	24	35
Consumer and other
Recorded Investment
With no related allowance recorded:	0	0	0	0	0
With an allowance recorded:	0	0	0	0	0
Total:	0	0	0	0	0
Unpaid Principal Balance
With no related allowance recorded:	0	0	0	0	0
With an allowance recorded:	0	0	0	0	0
Total:	0	0	0	0	0
Related Allowance	0	0	0	0	0
Average Recorded Investment
With no related allowance recorded:	0	0	0	0	0
With an allowance recorded:	0	0	0	18	10
Total:	0	0	0	18	10
Interest Income Recognized while Impaired
With no related allowance recorded:	0	0	0	0	0
With an allowance recorded:	0	0	0	3	3
Total:	$ 0	$ 0	$ 0	$ 3	$ 3