Allowance for Loan Losses - Allowance for Loan Loss Activity by Class (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 10,729	$ 10,138	$ 10,138
Charge offs	318	327	1,618
Recoveries	46	56	209
Provision for loan losses	500	500	2,000
Ending balance	10,957	10,367	10,729
Ending balance specifically evaluated for impairment	2,206	768	1,812
Ending balance collectively evaluated for impairment	8,751	9,599	8,917
Total	1,188,002	1,089,735	1,164,139
Ending balance specifically evaluated for impairment	31,715	27,852	31,392
Ending balance collectively evaluated for impairment	1,156,287	1,061,883	1,132,747
Commercial \| Real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	3,872	3,988	3,988
Charge offs	0	164	587
Recoveries	0	0	0
Provision for loan losses	(140)	191	471
Ending balance	3,732	4,015	3,872
Ending balance specifically evaluated for impairment	254	351	224
Ending balance collectively evaluated for impairment	3,478	3,664	3,648
Total	339,306	304,663	323,809
Ending balance specifically evaluated for impairment	8,951	10,671	7,790
Ending balance collectively evaluated for impairment	330,355	293,992	316,019
Commercial \| Construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	434	396	396
Charge offs	0	0	0
Recoveries	0	0	0
Provision for loan losses	(38)	45	38
Ending balance	396	441	434
Ending balance specifically evaluated for impairment	0	101	0
Ending balance collectively evaluated for impairment	396	340	434
Total	43,813	28,775	38,056
Ending balance specifically evaluated for impairment	741	763	741
Ending balance collectively evaluated for impairment	43,072	28,012	37,315
Commercial \| Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	3,358	1,780	1,780
Charge offs	17	0	212
Recoveries	6	11	49
Provision for loan losses	193	134	1,741
Ending balance	3,540	1,925	3,358
Ending balance specifically evaluated for impairment	1,664	39	1,309
Ending balance collectively evaluated for impairment	1,876	1,886	2,049
Total	177,783	158,507	181,528
Ending balance specifically evaluated for impairment	9,440	1,710	9,918
Ending balance collectively evaluated for impairment	168,343	156,797	171,610
Municipal
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	20	18	18
Charge offs	0	0	0
Recoveries	0	0	0
Provision for loan losses	1	0	2
Ending balance	21	18	20
Ending balance specifically evaluated for impairment	0	0	0
Ending balance collectively evaluated for impairment	21	18	20
Total	35,463	28,327	33,391
Ending balance specifically evaluated for impairment	0	0	0
Ending balance collectively evaluated for impairment	35,463	28,327	33,391
Residential \| Construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	36	44	44
Charge offs	0	0	0
Recoveries	0	0	0
Provision for loan losses	(5)	(20)	(8)
Ending balance	31	24	36
Ending balance specifically evaluated for impairment	0	0	0
Ending balance collectively evaluated for impairment	31	24	36
Total	15,847	13,717	17,868
Ending balance specifically evaluated for impairment	0	0	0
Ending balance collectively evaluated for impairment	15,847	13,717	17,868
Residential \| Term
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,130	1,288	1,288
Charge offs	81	53	456
Recoveries	4	14	40
Provision for loan losses	76	(280)	258
Ending balance	1,129	969	1,130
Ending balance specifically evaluated for impairment	272	251	255
Ending balance collectively evaluated for impairment	857	718	875
Total	439,984	421,202	432,661
Ending balance specifically evaluated for impairment	11,528	13,260	11,748
Ending balance collectively evaluated for impairment	428,456	407,942	420,913
Home equity line of credit
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	692	807	807
Charge offs	115	7	28
Recoveries	11	0	11
Provision for loan losses	128	11	(98)
Ending balance	716	811	692
Ending balance specifically evaluated for impairment	16	26	24
Ending balance collectively evaluated for impairment	700	785	668
Total	110,298	110,016	111,302
Ending balance specifically evaluated for impairment	1,039	1,448	1,179
Ending balance collectively evaluated for impairment	109,259	108,568	110,123
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	545	559	559
Charge offs	105	103	335
Recoveries	25	31	109
Provision for loan losses	116	86	212
Ending balance	581	573	545
Ending balance specifically evaluated for impairment	0	0	0
Ending balance collectively evaluated for impairment	581	573	545
Total	25,508	24,528	25,524
Ending balance specifically evaluated for impairment	16	0	16
Ending balance collectively evaluated for impairment	25,492	24,528	25,508
Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	642	1,258	1,258
Charge offs	0	0	0
Recoveries	0	0	0
Provision for loan losses	169	333	(616)
Ending balance	811	1,591	642
Ending balance specifically evaluated for impairment	0	0	0
Ending balance collectively evaluated for impairment	811	1,591	642
Total	0	0	0
Ending balance specifically evaluated for impairment	0	0	0
Ending balance collectively evaluated for impairment	$ 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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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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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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