Debt and Borrowing Arrangements (Details 5) (USD $)	3 Months Ended			1 Months Ended				1 Months Ended	3 Months Ended	1 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012 Amended credit facility	Jan. 31, 2012 4.0% Convertible senior notes due 2012	Mar. 31, 2012 4.0% Convertible senior notes due 2012	Mar. 31, 2012 4.0% Convertible senior notes due 2014	Dec. 31, 2011 4.0% Convertible senior notes due 2014	Jan. 31, 2012 6.00% Convertible Senior Notes due 2017 D	Mar. 31, 2012 6.00% Convertible Senior Notes due 2017 D	Jan. 31, 2012 6.00% Convertible Senior Notes due 2017 Maximum
Debt and Borrowing Arrangements
Borrowing capacity			$ 525,000,000
Principal amount of notes					199,000,000	250,000,000			250,000,000
Unamortized discount						36,000,000	40,000,000	63,000,000	61,000,000
Effective interest rate (as a percent)						13.00%			13.00%
Debt issued								250,000,000
Debt issuance cost	7,000,000	4,000,000						1,000,000
Proceeds from issuance of unnsecured debt	243,000,000	45,000,000						243,000,000
Liability component of notes								188,000,000
Equity component of notes								33,000,000
Conversion price of shares (in dollars per share)								$ 12.79
Conversion ratio, number of shares per $1,000 principal amount, numerator								78.2014		97.7517
Conversion ratio, principal amount, denominator										1,000
Number of business days preceding the maturity date during which holders of convertible notes may convert all or any portion of the notes									5
Number of consecutive business days during which the conversion price exceed the principal amount in order for the notes to be redeemable (in days)									5
Interest rate (as a percent)					4.00%	4.00%			6.00%
Debt purchased				51,000,000
Underwriting discount percentage								3.00%
Deferred taxes on equity component								$ 22,000,000
Percentage of the last reported sales price of the entity's common stock that the conversion price must equal or exceed per conversion eligibility terms, minimum								98.00%
Number of trading days within 30 consecutive trading days required per the conversion eligibility terms, minimum								20
Number of consecutive trading days required per the conversion eligibility terms, minimum								30
Percentage of the last reported sales price of the entity's common stock that the conversion price must equal or exceed per conversion eligibility terms, minimum								130.00%