Debt (Convertible Senior Notes) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Short-term Debt [Line Items]
Equity component related to repurchases, convertible, effective interest rate	1.875%		1.875%
Common stock shares issuable	109,357,000		109,357,000		114,832,000
Subsidiaries [Member]
Short-term Debt [Line Items]
Proceeds from (repayments of) notes payable			$ 17,000,000
Principal amount, aggregate repurchased	15,000,000		15,000,000
Convertible Senior Notes Due 2013 [Member]
Short-term Debt [Line Items]
Debt instrument, issuance date			May 16, 2008
Convertible senior notes issued			550,000,000
Equity component related to repurchases, convertible, effective interest rate	1.875%		1.875%
Interest payable dates			May 1 and November 1
Debt instrument, maturity date			May 01, 2013
Convertible senior notes effective interest rate, maximum	9.40%		9.40%
Conversion rate, in shares			24.1196
Common stock principal amount	1,000		1,000
Per share conversion price	$ 41.46		$ 41.46
Conversion premium			20.00%
Last reported selling price			$ 34.55
Initial strike price of warrants			$ 41.46
Upper strike price of warrants			$ 67.37
Terminated convertible note hedge transaction			55.00%
Common stock shares issuable	13,265,780		13,265,780
Carrying amount of the equity component	156,600,000		156,600,000
Senior notes amount outstanding			535,000,000
Principal balance	535,000,000		535,000,000		550,000,000
Debt discount	(58,737,000)		(58,737,000)		(86,030,000)
Carrying value	476,263,000		476,263,000		463,970,000
Cash interest expense	2,500,000	2,600,000	7,600,000	7,700,000
Non-cash interest expense	8,500,000	8,000,000	25,100,000	23,400,000
Convertible Senior Notes Due 2014 [Member]
Short-term Debt [Line Items]
Debt instrument, issuance date			April 24, 2009
Convertible senior notes issued			500,000,000
Equity component related to repurchases, convertible, effective interest rate	4.00%		4.00%
Interest payable dates			April 1 and October 1
Debt instrument, maturity date			Oct. 01, 2014
Convertible senior notes effective interest rate, maximum	13.00%		13.00%
Conversion rate, in shares			32.9164
Common stock principal amount	1,000		1,000
Per share conversion price	$ 30.38		$ 30.38
Conversion premium			22.50%
Last reported selling price			$ 24.80
Initial strike price of warrants			$ 30.38
Upper strike price of warrants			$ 44.64
Carrying amount of the equity component	169,000,000		169,000,000
Principal balance	500,000,000		500,000,000		500,000,000
Debt discount	(110,029,000)		(110,029,000)		(131,537,000)
Carrying value	389,971,000		389,971,000		368,463,000
Cash interest expense	5,000,000	5,000,000	15,000,000	15,000,000
Non-cash interest expense	$ 7,400,000	$ 6,500,000	$ 21,500,000	$ 18,900,000
Debt instrument, interest rate effective percentage before debt discount amortization			4.00%