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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 10,611	$ 10,198	$ 10,138	$ 9,916	$ 9,916
Charge offs	401	340	1,018	1,006	1,721
Recoveries	52	65	142	263	343
Provision for loan losses	750	375	1,750	1,125	1,600
Ending balance	11,012	10,298	11,012	10,298	10,138
Ending balance specifically evaluated for impairment	1,916	949	1,916	949	974
Ending balance collectively evaluated for impairment	9,096	9,349	9,096	9,349	9,164
Total	1,121,086	1,028,992	1,121,086	1,028,992	1,071,526
Ending balance specifically evaluated for impairment	35,060	28,185	35,060	28,185	27,583
Ending balance collectively evaluated for impairment	1,086,026	1,000,807	1,086,026	1,000,807	1,043,943
Commercial \| Real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	3,996	3,955	3,988	3,120	3,120
Charge offs	0	0	305	33	294
Recoveries	0	0	0	0	0
Provision for loan losses	8	84	321	952	1,162
Ending balance	4,004	4,039	4,004	4,039	3,988
Ending balance specifically evaluated for impairment	347	381	347	381	505
Ending balance collectively evaluated for impairment	3,657	3,658	3,657	3,658	3,483
Total	301,227	297,808	301,227	297,808	302,506
Ending balance specifically evaluated for impairment	9,836	10,442	9,836	10,442	10,021
Ending balance collectively evaluated for impairment	291,391	287,366	291,391	287,366	292,485
Commercial \| Construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	517	318	396	580	580
Charge offs	0	17	0	75	75
Recoveries	0	4	0	4	8
Provision for loan losses	(14)	22	107	(182)	(117)
Ending balance	503	327	503	327	396
Ending balance specifically evaluated for impairment	108	99	108	99	100
Ending balance collectively evaluated for impairment	395	228	395	228	296
Total	32,893	18,828	32,893	18,828	25,406
Ending balance specifically evaluated for impairment	763	788	763	788	763
Ending balance collectively evaluated for impairment	32,130	18,040	32,130	18,040	24,643
Commercial \| Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	2,171	1,778	1,780	1,452	1,452
Charge offs	0	137	58	167	376
Recoveries	7	24	25	80	129
Provision for loan losses	1,045	23	1,476	323	575
Ending balance	3,223	1,688	3,223	1,688	1,780
Ending balance specifically evaluated for impairment	1,130	68	1,130	68	39
Ending balance collectively evaluated for impairment	2,093	1,620	2,093	1,620	1,741
Total	172,986	131,198	172,986	131,198	150,769
Ending balance specifically evaluated for impairment	10,250	1,254	10,250	1,254	1,743
Ending balance collectively evaluated for impairment	162,736	129,944	162,736	129,944	149,026
Municipal
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	19	17	18	17	17
Charge offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision for loan losses	1	1	2	1	1
Ending balance	20	18	20	18	18
Ending balance specifically evaluated for impairment	0	0	0	0	0
Ending balance collectively evaluated for impairment	20	18	20	18	18
Total	33,311	26,153	33,311	26,153	27,056
Ending balance specifically evaluated for impairment	0	0	0	0	0
Ending balance collectively evaluated for impairment	33,311	26,153	33,311	26,153	27,056
Residential \| Construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	26	34	44	24	24
Charge offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision for loan losses	5	3	(13)	13	20
Ending balance	31	37	31	37	44
Ending balance specifically evaluated for impairment	0	0	0	0	0
Ending balance collectively evaluated for impairment	31	37	31	37	44
Total	15,495	14,269	15,495	14,269	18,303
Ending balance specifically evaluated for impairment	0	0	0	0	0
Ending balance collectively evaluated for impairment	15,495	14,269	15,495	14,269	18,303
Residential \| Term
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	999	1,365	1,288	1,391	1,391
Charge offs	281	72	351	338	379
Recoveries	10	14	29	88	93
Provision for loan losses	429	52	191	218	183
Ending balance	1,157	1,359	1,157	1,359	1,288
Ending balance specifically evaluated for impairment	307	318	307	318	304
Ending balance collectively evaluated for impairment	850	1,041	850	1,041	984
Total	429,572	403,159	429,572	403,159	411,469
Ending balance specifically evaluated for impairment	12,641	14,131	12,641	14,131	13,669
Ending balance collectively evaluated for impairment	416,931	389,028	416,931	389,028	397,800
Home equity line of credit
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	684	880	807	893	893
Charge offs	0	25	28	147	147
Recoveries	1	1	4	3	5
Provision for loan losses	2	18	(96)	125	56
Ending balance	687	874	687	874	807
Ending balance specifically evaluated for impairment	24	32	24	32	26
Ending balance collectively evaluated for impairment	663	842	663	842	781
Total	110,178	111,994	110,178	111,994	110,907
Ending balance specifically evaluated for impairment	1,519	1,400	1,519	1,400	1,387
Ending balance collectively evaluated for impairment	108,659	110,594	108,659	110,594	109,520
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	529	635	559	566	566
Charge offs	120	89	276	246	450
Recoveries	34	22	84	88	108
Provision for loan losses	92	50	168	210	335
Ending balance	535	618	535	618	559
Ending balance specifically evaluated for impairment	0	51	0	51	0
Ending balance collectively evaluated for impairment	535	567	535	567	559
Total	25,424	25,583	25,424	25,583	25,110
Ending balance specifically evaluated for impairment	51	170	51	170	0
Ending balance collectively evaluated for impairment	25,373	25,413	25,373	25,413	25,110
Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,670	1,216	1,258	1,873	1,873
Charge offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision for loan losses	(818)	122	(406)	(535)	(615)
Ending balance	852	1,338	852	1,338	1,258
Ending balance specifically evaluated for impairment	0	0	0	0	0
Ending balance collectively evaluated for impairment	852	1,338	852	1,338	1,258
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.

+ References

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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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- Definition

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

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