Loans and Allowance for Loan Losses - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Allowance for loan losses:
Beginning balance	$ 15,813	$ 15,232	$ 15,767	$ 15,442
Provision for loan losses	0	0	0	0
Charge-offs	0	(6)	(5)	(292)
Recoveries	4	22	55	98
Ending balance	15,817	15,248	15,817	15,248
Ending ALLL related to loans collectively evaluated for impairment	15,290		15,290		$ 15,254
Ending ALLL related to loans individually evaluated for impairment	527		527		513
Ending ALLL	15,817		15,817		15,767
Collectively evaluated for impairment	1,711,211		1,711,211		1,659,972
Individually evaluated for impairment	15,531		15,531		16,926
Total loans	$ 1,728,871		$ 1,728,871		$ 1,679,013
Ratio of allowance for loan losses to total loans	0.91%		0.91%		0.94%
Allowance for loan losses to non-accrual loans	4098.00%		4098.00%		3883.00%
Purchased credit-impaired
Allowance for loan losses:
Ending ALLL	$ 0		$ 0		$ 0
Purchased credit-impaired	2,129		2,129		2,115
Commercial loans \| Commercial and industrial
Allowance for loan losses:
Beginning balance	2,597	3,932	3,654	3,248
Provision for loan losses	(245)	612	(1,308)	1,509
Charge-offs	0	(5)	(3)	(289)
Recoveries	4	21	13	92
Ending balance	2,356	4,560	2,356	4,560
Ending ALLL related to loans collectively evaluated for impairment	2,183		2,183		3,604
Ending ALLL related to loans individually evaluated for impairment	173		173		50
Ending ALLL	2,356		2,356		3,654
Collectively evaluated for impairment	236,969		236,969		233,605
Individually evaluated for impairment	1,763		1,763		2,165
Total loans	$ 238,771		$ 238,771		$ 235,835
Ratio of allowance for loan losses to total loans	0.99%		0.99%		1.55%
Commercial loans \| Commercial and industrial \| Purchased credit-impaired
Allowance for loan losses:
Ending ALLL	$ 0		$ 0		$ 0
Purchased credit-impaired	39		39		65
Commercial real estate loans \| Commercial real estate, owner-occupied
Allowance for loan losses:
Beginning balance	2,339	2,082	2,294	1,753
Provision for loan losses	83	(56)	128	273
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending balance	2,422	2,026	2,422	2,026
Ending ALLL related to loans collectively evaluated for impairment	2,194		2,194		2,106
Ending ALLL related to loans individually evaluated for impairment	228		228		188
Ending ALLL	2,422		2,422		2,294
Collectively evaluated for impairment	308,272		308,272		292,798
Individually evaluated for impairment	6,997		6,997		6,999
Total loans	$ 316,467		$ 316,467		$ 300,963
Ratio of allowance for loan losses to total loans	0.77%		0.77%		0.76%
Commercial real estate loans \| Commercial real estate, owner-occupied \| Purchased credit-impaired
Allowance for loan losses:
Ending ALLL	$ 0		$ 0		$ 0
Purchased credit-impaired	1,198		1,198		1,166
Commercial real estate loans \| Commercial real estate, investor
Allowance for loan losses:
Beginning balance	7,390	6,065	6,475	6,320
Provision for loan losses	46	33	961	(222)
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending balance	7,436	6,098	7,436	6,098
Ending ALLL related to loans collectively evaluated for impairment	7,392		7,392		6,316
Ending ALLL related to loans individually evaluated for impairment	44		44		159
Ending ALLL	7,436		7,436		6,475
Collectively evaluated for impairment	838,856		838,856		820,023
Individually evaluated for impairment	1,831		1,831		2,171
Total loans	$ 841,493		$ 841,493		$ 822,984
Ratio of allowance for loan losses to total loans	0.88%		0.88%		0.79%
Commercial real estate loans \| Commercial real estate, investor \| Purchased credit-impaired
Allowance for loan losses:
Ending ALLL	$ 0		$ 0		$ 0
Purchased credit-impaired	806		806		790
Commercial real estate loans \| Construction
Allowance for loan losses:
Beginning balance	508	411	681	781
Provision for loan losses	157	217	(16)	(153)
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending balance	665	628	665	628
Ending ALLL related to loans collectively evaluated for impairment	665		665		674
Ending ALLL related to loans individually evaluated for impairment	0		0		7
Ending ALLL	665		665		681
Collectively evaluated for impairment	66,049		66,049		60,859
Individually evaluated for impairment	2,690		2,690		2,969
Total loans	$ 68,739		$ 68,739		$ 63,828
Ratio of allowance for loan losses to total loans	0.97%		0.97%		1.07%
Commercial real estate loans \| Construction \| Purchased credit-impaired
Allowance for loan losses:
Ending ALLL	$ 0		$ 0		$ 0
Purchased credit-impaired	0		0		0
Residential loans \| Home equity
Allowance for loan losses:
Beginning balance	952	981	1,031	973
Provision for loan losses	(39)	21	(118)	29
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending balance	913	1,002	913	1,002
Ending ALLL related to loans collectively evaluated for impairment	908		908		1,025
Ending ALLL related to loans individually evaluated for impairment	5		5		6
Ending ALLL	913		913		1,031
Collectively evaluated for impairment	120,588		120,588		131,620
Individually evaluated for impairment	569		569		753
Total loans	$ 121,243		$ 121,243		$ 132,467
Ratio of allowance for loan losses to total loans	0.75%		0.75%		0.78%
Allowance for loan losses to non-accrual loans	287.00%		287.00%		254.00%
Residential loans \| Home equity \| Purchased credit-impaired
Allowance for loan losses:
Ending ALLL	$ 0		$ 0		$ 0
Purchased credit-impaired	86		86		94
Residential loans \| Other residential
Allowance for loan losses:
Beginning balance	746	509	536	454
Provision for loan losses	35	33	245	88
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending balance	781	542	781	542
Ending ALLL related to loans collectively evaluated for impairment	781		781		535
Ending ALLL related to loans individually evaluated for impairment	0		0		1
Ending ALLL	781		781		536
Collectively evaluated for impairment	112,397		112,397		94,378
Individually evaluated for impairment	986		986		1,148
Total loans	$ 113,383		$ 113,383		$ 95,526
Ratio of allowance for loan losses to total loans	0.69%		0.69%		0.56%
Residential loans \| Other residential \| Purchased credit-impaired
Allowance for loan losses:
Ending ALLL	$ 0		$ 0		$ 0
Purchased credit-impaired	0		0		0
Consumer loans \| Installment and other consumer
Allowance for loan losses:
Beginning balance	325	340	378	372
Provision for loan losses	5	(5)	(88)	(40)
Charge-offs	0	(1)	(2)	(3)
Recoveries	0	1	42	6
Ending balance	330	335	330	335
Ending ALLL related to loans collectively evaluated for impairment	253		253		276
Ending ALLL related to loans individually evaluated for impairment	77		77		102
Ending ALLL	330		330		378
Collectively evaluated for impairment	28,080		28,080		26,689
Individually evaluated for impairment	695		695		721
Total loans	$ 28,775		$ 28,775		$ 27,410
Ratio of allowance for loan losses to total loans	1.15%		1.15%		1.38%
Allowance for loan losses to non-accrual loans	485.00%		485.00%
Consumer loans \| Installment and other consumer \| Purchased credit-impaired
Allowance for loan losses:
Ending ALLL	$ 0		$ 0		$ 0
Purchased credit-impaired	0		0		0
Unallocated
Allowance for loan losses:
Beginning balance	956	912	718	1,541
Provision for loan losses	(42)	(855)	196	(1,484)
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending balance	914	$ 57	914	$ 57
Ending ALLL related to loans collectively evaluated for impairment	914		914		718
Ending ALLL related to loans individually evaluated for impairment	0		0		0
Ending ALLL	914		914		718
Collectively evaluated for impairment	0		0		0
Individually evaluated for impairment	0		0		0
Total loans	0		0		0
Unallocated \| Purchased credit-impaired
Allowance for loan losses:
Ending ALLL	0		0		0
Purchased credit-impaired	$ 0		$ 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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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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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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