Basis of Presentation Basis of Presentation (Earnings per share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015
Numerator:
Net income	$ 83,300	$ 54,971
Less: earnings distributed to participating securities	(285)	(188)
Less: undistributed earnings allocated to participating securities	(404)	(166)
Numerator for basic earnings per share	82,611	54,617
Add back: undistributed earnings allocated to participating securities	404	166
Less: undistributed earnings reallocated to participating securities	(401)	(165)
Numerator for diluted earnings per share	$ 82,614	$ 54,618
Denominator:
Basic shares outstanding (shares)	347,815	366,748
Effect of dilutive securities (shares)	2,662	3,362
Diluted shares outstanding (shares)	350,477	370,110
Earnings Per Share [Abstract]
Earnings Per Share, Basic (usd per share)	$ 0.24	$ 0.15
Earnings Per Share, Diluted (usd per share)	$ 0.24	$ 0.15

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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 share based payment arrangements using the treasury stock method.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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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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Net Income or Loss Available to Common Stockholders plus adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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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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