Impaired Loan Information by Portfolio (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impaired loans by loan portfolio
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	$ 1,342	$ 5,214	$ 1,930
Related Allowance	1,342	5,214	1,930
Recorded Investment	72,801	77,297	51,410
Unpaid Principal Balance	79,276	81,071	54,822
Average Recorded Investment	76,180	77,209	51,678
Interest Income Recognized	2,026	2,700	1,993
Commercial and Industrial [Member]
Impaired loans by loan portfolio
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	10	3,661	183
Commercial Real Estate [Member]
Impaired loans by loan portfolio
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	42	196	204
Construction Loans [Member]
Impaired loans by loan portfolio
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0	0	0
Small Business [Member]
Impaired loans by loan portfolio
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1	8	4
Residential Real Estate [Member]
Impaired loans by loan portfolio
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,007	1,086	1,278
Home Equity [Member]
Impaired loans by loan portfolio
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	265	242	238
Consumer Portfolio Segment [Member]
Impaired loans by loan portfolio
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	17	21	23
With No Related Allowance Recorded [Member]
Impaired loans by loan portfolio
Recorded Investment	57,373	49,745	24,403
Unpaid Principal Balance	62,867	52,377	26,276
Average Recorded Investment	60,380	48,814	24,774
Interest Income Recognized	1,449	1,764	835
Related Allowance	0	0	0
With No Related Allowance Recorded [Member] | Commercial and Industrial [Member]
Impaired loans by loan portfolio
Recorded Investment	34,267	28,776	2,613
Unpaid Principal Balance	38,329	29,772	3,002
Average Recorded Investment	36,631	26,472	3,024
Interest Income Recognized	446	927	71
Related Allowance	0	0	0
With No Related Allowance Recorded [Member] | Commercial Real Estate [Member]
Impaired loans by loan portfolio
Recorded Investment	13,245	11,628	12,008
Unpaid Principal Balance	14,374	12,891	13,128
Average Recorded Investment	13,683	12,744	11,676
Interest Income Recognized	559	437	375
Related Allowance	0	0	0
With No Related Allowance Recorded [Member] | Construction Loans [Member]
Impaired loans by loan portfolio
Recorded Investment			304
Unpaid Principal Balance			305
Average Recorded Investment			308
Related Allowance			0
With No Related Allowance Recorded [Member] | Small Business [Member]
Impaired loans by loan portfolio
Recorded Investment	556	494	527
Unpaid Principal Balance	619	569	618
Average Recorded Investment	569	534	584
Interest Income Recognized	21	20	22
Related Allowance	0	0	0
With No Related Allowance Recorded [Member] | Residential Real Estate [Member]
Impaired loans by loan portfolio
Recorded Investment	4,264	4,216	3,874
Unpaid Principal Balance	4,397	4,427	4,033
Average Recorded Investment	4,332	4,302	3,958
Interest Income Recognized	218	185	157
Related Allowance	0	0	0
With No Related Allowance Recorded [Member] | Home Equity [Member]
Impaired loans by loan portfolio
Recorded Investment	4,950	4,485	4,893
Unpaid Principal Balance	5,056	4,572	5,005
Average Recorded Investment	5,063	4,602	5,023
Interest Income Recognized	198	184	195
Related Allowance	0	0	0
With No Related Allowance Recorded [Member] | Consumer Portfolio Segment [Member]
Impaired loans by loan portfolio
Recorded Investment	91	146	184
Unpaid Principal Balance	92	146	185
Average Recorded Investment	102	160	201
Interest Income Recognized	7	11	15
Related Allowance	0	0	0
With Allowance Recorded [Member]
Impaired loans by loan portfolio
Recorded Investment	15,428	27,552	27,007
Unpaid Principal Balance	16,409	28,694	28,546
Average Recorded Investment	15,800	28,395	26,904
Interest Income Recognized	577	936	1,158
With Allowance Recorded [Member] | Commercial and Industrial [Member]
Impaired loans by loan portfolio
Recorded Investment	376	10,402	2,534
Unpaid Principal Balance	376	10,440	2,648
Average Recorded Investment	391	10,760	2,848
Interest Income Recognized	19	325	48
With Allowance Recorded [Member] | Commercial Real Estate [Member]
Impaired loans by loan portfolio
Recorded Investment	3,393	5,185	10,978
Unpaid Principal Balance	3,399	5,533	11,047
Average Recorded Investment	3,447	5,491	10,789
Interest Income Recognized	198	200	592
With Allowance Recorded [Member] | Small Business [Member]
Impaired loans by loan portfolio
Recorded Investment	147	377	494
Unpaid Principal Balance	153	392	523
Average Recorded Investment	238	408	535
Interest Income Recognized	14	21	30
With Allowance Recorded [Member] | Residential Real Estate [Member]
Impaired loans by loan portfolio
Recorded Investment	9,420	9,959	11,531
Unpaid Principal Balance	10,154	10,530	12,652
Average Recorded Investment	9,575	10,065	11,669
Interest Income Recognized	284	332	460
With Allowance Recorded [Member] | Home Equity [Member]
Impaired loans by loan portfolio
Recorded Investment	1,876	1,378	1,096
Unpaid Principal Balance	2,110	1,547	1,287
Average Recorded Investment	1,916	1,403	655
Interest Income Recognized	55	50	14
With Allowance Recorded [Member] | Consumer Portfolio Segment [Member]
Impaired loans by loan portfolio
Recorded Investment	216	251	374
Unpaid Principal Balance	217	252	389
Average Recorded Investment	233	268	408
Interest Income Recognized	$ 7	$ 8	$ 14