Basis of Presentation Basis of Presentation (Earnings per share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net income	$ 177,539	$ 128,470	$ 369,807	$ 329,530
Less: earnings distributed to participating securities	(294)	(269)	(899)	(836)
Less: undistributed earnings allocated to participating securities	(1,645)	(870)	(2,837)	(1,764)
Numerator for basic earnings per share	175,600	127,331	366,071	326,930
Add back: undistributed earnings allocated to participating securities	1,645	870	2,837	1,764
Less: undistributed earnings reallocated to participating securities	(1,636)	(865)	(2,820)	(1,751)
Numerator for diluted earnings per share	$ 175,609	$ 127,336	$ 366,088	$ 326,943
Denominator:
Basic shares outstanding (shares)	298,538	340,171	309,453	344,383
Effect of dilutive securities (shares)	1,690	2,250	1,861	2,557
Diluted shares outstanding (shares)	300,228	342,421	311,314	346,940
Earnings per share:
Basic earnings (usd per share)	$ 0.59	$ 0.37	$ 1.18	$ 0.95
Diluted earnings (usd per share)	$ 0.58	$ 0.37	$ 1.18	$ 0.94