Stock-Based Compensation - Stock Option Activity (Narratives) (Details) - Stock options $ in Millions	9 Months Ended
Sep. 30, 2018 USD ($)
Stock-Based Compensation
Intrinsic value of options exercised	$ 0.1
First anniversary vesting
Stock-Based Compensation
Vesting percentage	33.33%
Second anniversary vesting
Stock-Based Compensation
Vesting percentage	33.33%
Third anniversary vesting
Stock-Based Compensation
Vesting percentage	33.33%
Vesting period	3 years
Maximum
Stock-Based Compensation
Expiration period	7 years

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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-Section 50
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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-Section 50
-Paragraph 2
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Percentage of vesting of share-based compensation awards.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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