Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Net Income (Numerator)
Basic earnings per share - net income (in dollars)	$ 31,550	$ 72,303	$ 62,311	$ 110,882
5.125% convertible senior notes, net of tax (in dollars)		1,969		4,327
Diluted earnings per share - net income (in dollars)	$ 31,550	$ 74,272	$ 62,311	$ 115,209
Weighted average common shares outstanding (in shares)
Weighted average common shares outstanding (in shares)	241,900,000	226,220,000	241,718,000	224,615,000
Dilutive common share equivalents (in shares)	1,591,000	1,789,000	1,461,000	1,699,000
5.125% convertible senior notes, net of tax (in shares)		14,039,000		15,407,000
Weighted average common shares outstanding - diluted (in shares)	243,491,000	242,048,000	243,179,000	241,721,000
Per Share Amount
Basic (in dollars per share)	$ 0.13	$ 0.32	$ 0.26	$ 0.49
Diluted (in dollars per share)	$ 0.13	$ 0.31	$ 0.26	$ 0.48
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