Earnings Per Share (Details) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended			6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2013 Convertible Debt [Member]	Jun. 15, 2014 Convertible Debt [Member]	Jun. 12, 2014 Convertible Debt [Member]	Jun. 30, 2014 Employee And Directors Stock Options [Member]	Jun. 30, 2013 Employee And Directors Stock Options [Member]
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%
Antidilutive securities excluded from computation of earnings per share amount (in shares)					16,700,000			0	2,500,000
After-tax-equivalent of interest					$ 2,400,000
Net Income (Numerator)
Basic earnings - net income (loss) (in dollars)	72,303,000	28,958,000	110,882,000	77,173,000
5.125% convertible senior notes, net of tax (in dollars)	1,969,000		4,327,000	4,716,000
Diluted earnings - net income (loss) (in dollars)	$ 74,272,000	$ 28,958,000	$ 115,209,000	$ 81,889,000
Shares (Denominator)
Weighted average common shares outstanding (in shares)	226,220,000	220,471,000	224,615,000	220,233,000
Dilutive common share equivalents (in shares)	1,789,000	1,265,000	1,699,000	1,363,000
5.125% convertible senior notes, net of tax (in shares)	14,039,000		15,407,000	16,650,000
Weighted average common shares outstanding - diluted (in shares)	242,048,000	221,736,000	241,721,000	238,246,000
Per Share Amount
Basic earnings per share (in dollars per share)	$ 0.32	$ 0.13	$ 0.49	$ 0.35
Diluted earnings per share (in dollars per share)	$ 0.31	$ 0.13	$ 0.48	$ 0.34