Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net Income (Numerator)
Basic earnings per share - net income (in dollars)	$ 60,617	$ 91,173	$ 122,928	$ 202,055
5.125% convertible senior notes, net of tax (in dollars)				4,327
Diluted earnings per share - net income (in dollars)	$ 60,617	$ 91,173	$ 122,928	$ 206,382
Weighted average common shares outstanding (in shares)
Weighted average common shares outstanding (in shares)	242,074,000	240,087,000	241,836,000	229,772,000
Dilutive common share equivalents (in shares)	1,748,000	2,157,000	1,557,000	1,852,000
5.125% convertible senior notes, net of tax (in shares)				10,271,000
Weighted average common shares outstanding - diluted (in shares)	243,822,000	242,244,000	243,393,000	241,895,000
Per Share Amount
Basic (in dollars per share)	$ 0.25	$ 0.38	$ 0.51	$ 0.88
Diluted (in dollars per share)	$ 0.25	$ 0.38	$ 0.51	$ 0.85
Options
Antidilutive securities excluded from computation of earnings per share amount
Antidilutive securities excluded from computation of earnings per share amount (in shares)			0	0