Description of the Business and Summary of Significant Accounting Policies (Details 6) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net Income (Numerator)
Basic earnings (loss) - net income (loss) (in dollars)	$ 30,203,000	$ 43,304,000	$ 98,710,000	$ 105,903,000	$ 7,792,000	$ 18,741,000	$ 49,207,000	$ 64,969,000	$ 278,120,000	$ 140,709,000	$ (8,184,000)
Diluted earnings (loss) - net income (loss) (in dollars)									287,552,000	150,217,000	(8,184,000)
Shares (Denominator)
Weighted average common shares outstanding (in shares)									218,471,000	216,760,000	200,704,000
Dilutive stock option effect (in shares)									1,139,000	1,575,000
Weighted average common shares outstanding - diluted (in shares)									235,992,000	234,717,000	200,704,000
Per Share Amount
Basic earnings (loss) per share (in dollars per share)	$ 0.14	$ 0.20	$ 0.45	$ 0.49	$ 0.04	$ 0.09	$ 0.23	$ 0.30	$ 1.27	$ 0.65	$ (0.04)
Diluted earnings (loss) per share (in dollars per share)	$ 0.14	$ 0.19	$ 0.43	$ 0.46	$ 0.04	$ 0.09	$ 0.22	$ 0.29	$ 1.22	$ 0.64	$ (0.04)
5.125% convertible senior notes, due 2014
Antidilutive securities excluded from computation of earnings per share amount
After-tax equivalent of interest excluded from computation of earnings (in dollars)											5,000,000
Stated interest rate (as a percent)											5.125%
Weighted average equivalent shares											8,400,000
Net Income (Numerator)
5.125% convertible senior notes, net of tax (in dollars)									$ 9,432,000	$ 9,508,000
Shares (Denominator)
5.125% convertible senior notes, net of tax (in shares)									16,382,000	16,382,000
Options
Antidilutive securities excluded from computation of earnings per share amount
Antidilutive securities excluded from computation of earnings per share amount (per shares)									4,000,000	3,100,000	2,100,000