Earnings Per Share - Schedule of Dilutive Effect of Stock Options RSUs and PSAs (Details) - shares shares in Thousands	3 Months Ended	12 Months Ended
Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Basic weighted-average shares outstanding	18,838	18,873	18,806	18,670	18,646	18,666	18,775	18,972	18,797	18,766	18,989
Effect of potential exercise of stock options, RSUs, and performance shares									538	478	427
Diluted weighted-average shares outstanding	19,333	19,306	19,209	19,158	19,136	19,024	19,086	19,423	19,335	19,244	19,416

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

+ References

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- Definition

The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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