Stock-Based Compensation Plans - Restricted stock activity (Details) - USD ($)	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
The 2007 plan
Number Outstanding
Number of shares available	885,730
The 2007 plan \| Restricted Stock
Number Outstanding
Balance at the beginning of the period (in shares)	328,122
Shares forfeited	(2,400)
Shares vested	(167,870)
Balance at the end of the period (in shares)	425,306
The 2007 plan \| Restricted Stock \| Awards Vesting Over Less Than One Year
Number Outstanding
Shares granted	267,454
Employee Stock Purchase Plan
Number Outstanding
Shares issued	11,284	11,485
Maximum percentage of cash compensation allowed to be deducted for the purchase of common stock by eligible employees	10.00%
Maximum number of shares to be purchased by employee in one calendar year	1,000
Maximum amount of shares to be purchased by employee in one calendar year (in dollars)	$ 25,000
Purchase price expressed as a percentage of the market price of the common stock on the purchase date or on the date of entry	85.00%
2018 Plan \| Restricted Stock
Number Outstanding
Shares granted	0

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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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.

+ References

No definition available.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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- Definition

The highest quantity of shares an employee can purchase under the plan per period.

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

Purchase price of common stock expressed as a percentage of its fair value.

+ References

No definition available.

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- Definition

Number of shares issued during the period as a result of an employee stock purchase plan.

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-Name Accounting Standards Codification
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- Definition

The maximum amount of shares an employee can purchase under the plan per period.

+ References

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- Definition

Represents the maximum percentage of cash compensation allowed to be deducted each pay period for the purchase of common stock by eligible employees.

+ References

No definition available.

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