Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Net Income (Numerator)
Basic earnings - net income (loss) (in dollars)	$ 48,215	$ 45,675
5.125% convertible senior notes, net of tax (in dollars)	2,358	2,358
Diluted earnings - net income (loss) (in dollars)	$ 50,573	$ 48,033
Shares (Denominator)
Weighted average common shares outstanding (in shares)	219,995,000	218,996,000
Dilutive common share equivalents (in shares)	1,460,000	1,148,000
5.125% convertible senior notes, net of tax (in shares)	16,632,000	16,382,000
Weighted average common shares outstanding - diluted (in shares)	238,087,000	236,526,000
Per Share Amount
Basic earnings per share (in dollars per share)	$ 0.22	$ 0.21
Diluted earnings per share (in dollars per share)	$ 0.21	$ 0.20
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%	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)	3,000,000	3,900,000