Loans and Allowance for Loan Losses - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 15,442	$ 14,999	$ 15,099
Provision (reversal)	500	(1,850)	500
Charge-offs	(293)	(36)	(864)
Recoveries	118	2,329	264
Ending balance	15,767	15,442	14,999
Ending ALLL related to loans collectively evaluated for impairment	15,254	14,451
Ending ALLL related to loans individually evaluated for impairment	513	991
Ending ALLL	15,767	15,442
Recorded Investment:
Collectively evaluated for impairment	1,659,972	1,465,383
Individually evaluated for impairment	16,926	18,313
Total loans	$ 1,679,013	$ 1,486,616
Ratio of allowance for loan losses to total loans	0.94%	1.04%
Allowance for loan losses to non-accrual loans	3883.00%	10650.00%
Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	2,115	2,920
Commercial \| Commercial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	3,248	3,023	2,837
Provision (reversal)	584	93	(45)
Charge-offs	(289)	(11)	(5)
Recoveries	111	143	236
Ending balance		3,248	3,023
Ending ALLL related to loans collectively evaluated for impairment	3,604	2,963
Ending ALLL related to loans individually evaluated for impairment	50	285
Ending ALLL	3,654	3,248
Recorded Investment:
Collectively evaluated for impairment	233,605	216,368
Individually evaluated for impairment	2,165	2,207
Total loans	$ 235,835	$ 218,615
Ratio of allowance for loan losses to total loans	1.55%	1.49%
Commercial \| Commercial and industrial \| Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	65	40
Commercial real estate \| Commercial real estate, owner-occupied
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,753	2,249	1,924
Provision (reversal)	541	(476)	325
Charge-offs	0	(20)	0
Recoveries	0	0	0
Ending balance		1,753	2,249
Ending ALLL related to loans collectively evaluated for impairment	2,106	1,590
Ending ALLL related to loans individually evaluated for impairment	188	163
Ending ALLL	2,294	1,753
Recorded Investment:
Collectively evaluated for impairment	292,798	239,648
Individually evaluated for impairment	6,999	6,993
Total loans	$ 300,963	$ 247,713
Ratio of allowance for loan losses to total loans	0.76%	0.71%
Commercial real estate \| Commercial real estate, owner-occupied \| Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	1,166	1,072
Commercial real estate \| Commercial real estate, investor
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	6,320	6,178	6,672
Provision (reversal)	155	(2,014)	(517)
Charge-offs	0	0	0
Recoveries	0	2,156	23
Ending balance		6,320	6,178
Ending ALLL related to loans collectively evaluated for impairment	6,316	5,945
Ending ALLL related to loans individually evaluated for impairment	159	375
Ending ALLL	6,475	6,320
Recorded Investment:
Collectively evaluated for impairment	820,023	720,266
Individually evaluated for impairment	2,171	2,256
Total loans	$ 822,984	$ 724,228
Ratio of allowance for loan losses to total loans	0.79%	0.87%
Commercial real estate \| Commercial real estate, investor \| Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	790	1,706
Commercial real estate \| Construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	781	724	839
Provision (reversal)	(100)	57	724
Charge-offs	0	0	(839)
Recoveries	0	0	0
Ending balance		781	724
Ending ALLL related to loans collectively evaluated for impairment	674	773
Ending ALLL related to loans individually evaluated for impairment	7	8
Ending ALLL	681	781
Recorded Investment:
Collectively evaluated for impairment	60,859	71,564
Individually evaluated for impairment	2,969	3,245
Total loans	$ 63,828	$ 74,809
Ratio of allowance for loan losses to total loans	1.07%	1.04%
Commercial real estate \| Construction \| Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	0	0
Residential loans \| Home equity
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	973	910	859
Provision (reversal)	58	60	48
Charge-offs	0	0	0
Recoveries	0	3	3
Ending balance		973	910
Ending ALLL related to loans collectively evaluated for impairment	1,025	966
Ending ALLL related to loans individually evaluated for impairment	6	7
Ending ALLL	1,031	973
Recorded Investment:
Collectively evaluated for impairment	131,620	116,390
Individually evaluated for impairment	753	715
Total loans	$ 132,467	$ 117,207
Ratio of allowance for loan losses to total loans	0.78%	0.83%
Allowance for loan losses to non-accrual loans	254.00%	1071.00%
Residential loans \| Home equity \| Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	94	102
Residential loans \| Other residential
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	454	394	433
Provision (reversal)	82	60	(39)
Charge-offs	0	0	0
Recoveries	0	0	0
Ending balance		454	394
Ending ALLL related to loans collectively evaluated for impairment	535	399
Ending ALLL related to loans individually evaluated for impairment	1	55
Ending ALLL	536	454
Recorded Investment:
Collectively evaluated for impairment	94,378	76,584
Individually evaluated for impairment	1,148	1,965
Total loans	$ 95,526	$ 78,549
Ratio of allowance for loan losses to total loans	0.56%	0.58%
Residential loans \| Other residential \| Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	0	0
Consumer loans \| Installment and other consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	372	425	566
Provision (reversal)	3	(75)	(123)
Charge-offs	(4)	(5)	(20)
Recoveries	7	27	2
Ending balance		372	425
Ending ALLL related to loans collectively evaluated for impairment	276	274
Ending ALLL related to loans individually evaluated for impairment	102	98
Ending ALLL	378	372
Recorded Investment:
Collectively evaluated for impairment	26,689	24,563
Individually evaluated for impairment	721	932
Total loans	$ 27,410	$ 25,495
Ratio of allowance for loan losses to total loans	1.38%	1.46%
Allowance for loan losses to non-accrual loans		683.00%
Consumer loans \| Installment and other consumer \| Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	0	0
Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,541	1,096	969
Provision (reversal)	(823)	445	127
Charge-offs	0	0	0
Recoveries	0	0	0
Ending balance		1,541	$ 1,096
Ending ALLL related to loans collectively evaluated for impairment	718	1,541
Ending ALLL related to loans individually evaluated for impairment	0	0
Ending ALLL	718	1,541
Recorded Investment:
Collectively evaluated for impairment	0	0
Individually evaluated for impairment	0	0
Total loans		0
Unallocated \| Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	0	0
Recorded Investment:
Purchased credit-impaired	$ 0	$ 0

Allowance as percentage of non-accrual loans.

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Allowance as percentage of total loans.

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

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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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A valuation allowance for financing receivables that are expected to be uncollectible.

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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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