Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012 5.125% convertible senior notes, due 2014	Dec. 31, 2011 5.125% convertible senior notes, due 2014	Mar. 31, 2012 Stock options	Mar. 31, 2011 Stock options
Antidilutive securities excluded from computation of earnings per share amount
Stated interest rate (as a percent)			5.125%	5.125%
Antidilutive securities excluded from computation of earnings per share amount (per shares)					3,900,000	1,200,000
Net Income (Numerator)
Basic earnings (loss) - net income (loss) (in dollars)	$ 45,675	$ 105,903
5.125% convertible senior notes, net of tax (in dollars)	2,358	2,358
Diluted earnings (loss) - net income (loss) (in dollars)	$ 48,033	$ 108,261
Shares (Denominator)
Weighted average common shares outstanding (in shares)	218,996,000	217,992,000
Dilutive stock option effect (in shares)	1,148,000	1,850,000
5.125% convertible senior notes, net of tax (in shares)	16,382,000	16,382,000
Weighted average common shares outstanding - diluted (in shares)	236,526,000	236,224,000
Per Share Amount
Basic earnings (loss) per share (in dollars per share)	$ 0.21	$ 0.49
Diluted earnings (loss) per share (in dollars per share)	$ 0.20	$ 0.46