Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Computation of basic and diluted earnings per share
Numerator for basic and diluted earnings per share - net income (loss) attributable to common stockholders	$ 437,671	$ 312,639
Denominator for basic earnings per share - weighted average shares	371,426	362,534
Effect of dilutive securities:
Employee stock options	15	70
Non-vested restricted shares	720	397
Redeemable shares	1,096	1,651
Dilutive potential common shares	1,831	2,118
Denominator for diluted earnings per share - adjusted weighted average shares	373,257	364,652
Basic earnings per share	$ 1.18	$ 0.86
Diluted earnings per share	$ 1.17	$ 0.86

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

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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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Computation of basic and diluted earnings per share.

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Incremental Common Shares Attributable to Employee stock options.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of operating partnership units.

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