Basis of Presentation (Earnings per share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Numerator:
Net income	$ 166,757	$ 170,751
Less: earnings distributed to participating securities	(308)	(296)
Less: undistributed earnings allocated to participating securities	(1,410)	(1,622)
Numerator for basic earnings per share	165,039	168,833
Add back: undistributed earnings allocated to participating securities	1,410	1,622
Less: undistributed earnings reallocated to participating securities	(1,407)	(1,614)
Numerator for diluted earnings per share	$ 165,042	$ 168,841
Denominator:
Basic shares outstanding (shares)	277,637	286,683
Effect of dilutive securities (shares)	1,003	1,343
Diluted shares outstanding (shares)	278,640	288,026
Earnings per share:
Basic earnings (usd per share)	$ 0.59	$ 0.59
Diluted earnings (usd per share)	$ 0.59	$ 0.59

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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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