Net Income per Share (Reconciliation Between Basic and Diluted Weighted Average Shares Outstanding) (Details) - shares shares in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Basic weighted average shares outstanding (in shares)	56,590	57,758	56,589	59,354
Effect of dilution:
Diluted weighted average shares outstanding (in shares)	57,335	58,387	57,529	60,044
Stock options
Effect of dilution:
Effect of dilution (in shares)	15	5	24	3
Restricted stock units
Effect of dilution:
Effect of dilution (in shares)	730	624	916	687

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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.

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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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