Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Net Income (Numerator)
Basic earnings - net income (loss) (in dollars)	$ 38,579	$ 48,215
5.125% convertible senior notes, net of tax (in dollars)	2,358	2,358
Diluted earnings - net income (loss) (in dollars)	$ 40,937	$ 50,573
Shares (Denominator)
Weighted average common shares outstanding (in shares)	223,011,000	219,995,000
Dilutive common share equivalents (in shares)	1,608,000	1,460,000
5.125% convertible senior notes, net of tax (in shares)	16,775,000	16,632,000
Weighted average common shares outstanding - diluted (in shares)	241,394,000	238,087,000
Per Share Amount
Basic earnings per share (in dollars per share)	$ 0.17	$ 0.22
Diluted earnings per share (in dollars per share)	$ 0.17	$ 0.21
5.125% convertible senior notes, due 2014
Antidilutive securities excluded from computation of earnings per share amount
Stated interest rate on convertible senior notes (as a percent)	5.125%
Options
Antidilutive securities excluded from computation of earnings per share amount
Antidilutive securities excluded from computation of earnings per share amount (in shares)	0	3,000,000