Summary of Significant Accounting Policies - EPS and New Accounting Principle (Details) - shares shares in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings per share
Basic weighted average number of shares outstanding	268,386	309,062	276,306	308,879
Diluted weighted average number of shares outstanding	268,386	309,137	276,306	309,082
Restricted stock and restricted stock unit
Earnings per share
Add: Dilutive effect of non-vested restricted stock units		33		48
Weighted Average Anti-dilutive Awards	6,165	2,284	5,697	1,877
Stock options
Earnings per share
Weighted Average Anti-dilutive Awards	454	538	454	554
Performance share unit awards
Earnings per share
Add: Dilutive effect of non-vested restricted stock units		42		155
Weighted Average Anti-dilutive Awards	1,595	2,592	1,595	1,996

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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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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