Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Computation of basic and diluted earnings per share
Numerator for basic and diluted earnings per share - net income (loss) attributable to common stockholders	$ 195,474	$ 312,573	$ 344,444	$ 503,373
Denominator for basic earnings per share - weighted average shares	356,646	350,399	355,879	343,624
Effect of dilutive securities:
Employee stock options	129	153	115	176
Non-vested restricted shares	465	471	359	444
Redeemable shares	1,651	0	1,136	0
Convertible senior unsecured notes	0	343	0	379
Dilutive potential common shares	2,245	967	1,610	999
Denominator for diluted earnings per share - adjusted weighted average shares	358,891	351,366	357,489	344,623
Basic earnings per share	$ 0.55	$ 0.89	$ 0.97	$ 1.46
Diluted earnings per share	$ 0.54	$ 0.89	$ 0.96	$ 1.46

Computation of basic and diluted earnings per share.

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Incremental Common Shares Attributable to Employee stock options.

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Incremental Common Shares Attributable to Nonvested restricted shares.

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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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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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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of convertible debt securities using the if-converted method.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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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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