Earnings per Share (Reconciliation of Denominator for Basic and Diluted Earnings Per Share) (Details) - $ / shares	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Weighted average common shares—basic	128,793,661	131,664,296	129,519,577	132,301,814
Incremental shares from assumed exercise of options	586,295	456,939	584,320	484,720
Weighted average common shares-diluted	129,379,956	132,121,235	130,103,897	132,786,534
Earnings per share: Basic (usd per share)	$ 0.51	$ 1.39	$ 2.31	$ 4.04
Earnings per share: Diluted (usd per share)	$ 0.51	$ 1.39	$ 2.29	$ 4.02

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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 call options and warrants 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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