Earnings Per Share (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net Income (Numerator)
Basic earnings - net income (loss) (in dollars)	$ 57,486,000	$ 12,833,000	$ 134,659,000	$ 102,980,000
5.125% convertible senior notes, net of tax (in dollars)	2,358,000		7,074,000	7,074,000
Diluted earnings - net income (loss) (in dollars)	59,844,000	12,833,000	141,733,000	110,054,000
Shares (Denominator)
Weighted average common shares outstanding (in shares)	220,926,000	219,191,000	220,464,000	219,097,000
Dilutive common share equivalents (in shares)	1,366,000	853,000	1,363,000	908,000
5.125% convertible senior notes, net of tax (in shares)	16,709,000		16,670,000	16,531,000
Weighted average common shares outstanding - diluted (in shares)	239,001,000	220,044,000	238,497,000	236,536,000
Per Share Amount
Basic earnings per share (in dollars per share)	$ 0.26	$ 0.06	$ 0.61	$ 0.47
Diluted earnings per share (in dollars per share)	$ 0.25	$ 0.06	$ 0.59	$ 0.47
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%	5.125%	5.125%
Antidilutive securities excluded from computation of earnings per share amount (in shares)		16,600,000
After-tax equivalent of interest (in dollars)		$ 2,400,000
Options
Antidilutive securities excluded from computation of earnings per share amount
Antidilutive securities excluded from computation of earnings per share amount (in shares)			2,400,000	6,500,000