Basis of Presentation Basis of Presentation (Earnings per share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accounting Policies [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			100	2,300
Numerator:
Net income	$ 100,749	$ 117,760	$ 192,268	$ 201,060
Less: earnings distributed to participating securities	(300)	(283)	(605)	(568)
Less: undistributed earnings allocated to participating securities	(772)	(791)	(1,330)	(1,064)
Numerator for basic earnings per share	99,677	116,686	190,333	199,428
Add back: undistributed earnings allocated to participating securities	772	791	1,330	1,064
Less: undistributed earnings reallocated to participating securities	(768)	(785)	(1,322)	(1,055)
Numerator for diluted earnings per share	$ 99,681	$ 116,692	$ 190,341	$ 199,437
Denominator:
Basic shares outstanding (shares)	312,315	345,240	315,021	346,528
Effect of dilutive securities (shares)	1,565	2,759	1,946	2,710
Diluted shares outstanding (shares)	313,880	347,999	316,967	349,238
Earnings per share:
Basic earnings (usd per share)	$ 0.32	$ 0.34	$ 0.60	$ 0.58
Diluted earnings (usd per share)	$ 0.32	$ 0.34	$ 0.60	$ 0.57