Allowance for Loan Losses - Allowance for Loan Loss Activity by Class (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 11,472	$ 10,611	$ 10,729	$ 10,138	$ 10,138
Charge offs	223	401	596	1,018	1,618
Recoveries	100	52	216	142	209
Provision for loan losses	333	750	1,333	1,750	2,000
Ending balance	11,682	11,012	11,682	11,012	10,729
Ending balance specifically evaluated for impairment	2,402	1,916	2,402	1,916	1,812
Ending balance collectively evaluated for impairment	9,280	9,096	9,280	9,096	8,917
Total	1,243,558	1,121,086	1,243,558	1,121,086	1,164,139
Ending balance specifically evaluated for impairment	32,098	35,060	32,098	35,060	31,392
Ending balance collectively evaluated for impairment	1,211,460	1,086,026	1,211,460	1,086,026	1,132,747
Commercial \| Real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	3,732	3,996	3,872	3,988	3,988
Charge offs	0	0	0	305	587
Recoveries	52	0	52	0	0
Provision for loan losses	(195)	8	(335)	321	471
Ending balance	3,589	4,004	3,589	4,004	3,872
Ending balance specifically evaluated for impairment	265	347	265	347	224
Ending balance collectively evaluated for impairment	3,324	3,657	3,324	3,657	3,648
Total	366,390	301,227	366,390	301,227	323,809
Ending balance specifically evaluated for impairment	9,410	9,836	9,410	9,836	7,790
Ending balance collectively evaluated for impairment	356,980	291,391	356,980	291,391	316,019
Commercial \| Construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	399	517	434	396	396
Charge offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision for loan losses	(185)	(14)	(220)	107	38
Ending balance	214	503	214	503	434
Ending balance specifically evaluated for impairment	0	108	0	108	0
Ending balance collectively evaluated for impairment	214	395	214	395	434
Total	23,889	32,893	23,889	32,893	38,056
Ending balance specifically evaluated for impairment	741	763	741	763	741
Ending balance collectively evaluated for impairment	23,148	32,130	23,148	32,130	37,315
Commercial \| Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	3,475	2,171	3,358	1,780	1,780
Charge offs	51	0	68	58	212
Recoveries	23	7	33	25	49
Provision for loan losses	144	1,045	268	1,476	1,741
Ending balance	3,591	3,223	3,591	3,223	3,358
Ending balance specifically evaluated for impairment	1,890	1,130	1,890	1,130	1,309
Ending balance collectively evaluated for impairment	1,701	2,093	1,701	2,093	2,049
Total	188,128	172,986	188,128	172,986	181,528
Ending balance specifically evaluated for impairment	9,849	10,250	9,849	10,250	9,918
Ending balance collectively evaluated for impairment	178,279	162,736	178,279	162,736	171,610
Municipal
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	21	19	20	18	18
Charge offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision for loan losses	2	1	3	2	2
Ending balance	23	20	23	20	20
Ending balance specifically evaluated for impairment	0	0	0	0	0
Ending balance collectively evaluated for impairment	23	20	23	20	20
Total	56,704	33,311	56,704	33,311	33,391
Ending balance specifically evaluated for impairment	0	0	0	0	0
Ending balance collectively evaluated for impairment	56,704	33,311	56,704	33,311	33,391
Residential \| Construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	29	26	36	44	44
Charge offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision for loan losses	7	5	0	(13)	(8)
Ending balance	36	31	36	31	36
Ending balance specifically evaluated for impairment	0	0	0	0	0
Ending balance collectively evaluated for impairment	36	31	36	31	36
Total	18,166	15,495	18,166	15,495	17,868
Ending balance specifically evaluated for impairment	0	0	0	0	0
Ending balance collectively evaluated for impairment	18,166	15,495	18,166	15,495	17,868
Residential \| Term
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,138	999	1,130	1,288	1,288
Charge offs	116	281	212	351	456
Recoveries	3	10	45	29	40
Provision for loan losses	67	429	129	191	258
Ending balance	1,092	1,157	1,092	1,157	1,130
Ending balance specifically evaluated for impairment	238	307	238	307	255
Ending balance collectively evaluated for impairment	854	850	854	850	875
Total	459,449	429,572	459,449	429,572	432,661
Ending balance specifically evaluated for impairment	10,928	12,641	10,928	12,641	11,748
Ending balance collectively evaluated for impairment	448,521	416,931	448,521	416,931	420,913
Home equity line of credit
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	678	684	692	807	807
Charge offs	6	0	121	28	28
Recoveries	0	1	13	4	11
Provision for loan losses	47	2	135	(96)	(98)
Ending balance	719	687	719	687	692
Ending balance specifically evaluated for impairment	7	24	7	24	24
Ending balance collectively evaluated for impairment	712	663	712	663	668
Total	105,213	110,178	105,213	110,178	111,302
Ending balance specifically evaluated for impairment	1,168	1,519	1,168	1,519	1,179
Ending balance collectively evaluated for impairment	104,045	108,659	104,045	108,659	110,123
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	575	529	545	559	559
Charge offs	50	120	195	276	335
Recoveries	22	34	73	84	109
Provision for loan losses	193	92	317	168	212
Ending balance	740	535	740	535	545
Ending balance specifically evaluated for impairment	2	0	2	0	0
Ending balance collectively evaluated for impairment	738	535	738	535	545
Total	25,619	25,424	25,619	25,424	25,524
Ending balance specifically evaluated for impairment	2	51	2	51	16
Ending balance collectively evaluated for impairment	25,617	25,373	25,617	25,373	25,508
Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,425	1,670	642	1,258	1,258
Charge offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision for loan losses	253	(818)	1,036	(406)	(616)
Ending balance	1,678	852	1,678	852	642
Ending balance specifically evaluated for impairment	0	0	0	0	0
Ending balance collectively evaluated for impairment	1,678	852	1,678	852	642
Total	0	0	0	0	0
Ending balance specifically evaluated for impairment	0	0	0	0	0
Ending balance collectively evaluated for impairment	$ 0	$ 0	$ 0	$ 0	$ 0

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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The balance of financing receivables that were collectively evaluated for impairment.

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Amount of expense related to estimated loss from loan and lease transactions.

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