Debt (Convertible Senior Notes) (Details) (USD $)	3 Months Ended		0 Months Ended						0 Months Ended	3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Nov. 07, 2008 Convertible Senior Notes 1.875% Due 2013 [Member]	May 16, 2008 Convertible Senior Notes 1.875% Due 2013 [Member]	May 16, 2008 Convertible Senior Notes 1.875% Due 2013 [Member]	Mar. 31, 2012 Convertible Senior Notes 1.875% Due 2013 [Member]	Dec. 31, 2011 Convertible Senior Notes 1.875% Due 2013 [Member]	Mar. 31, 2011 Convertible Senior Notes 1.875% Due 2013 [Member]	Apr. 24, 2009 Convertible Senior Notes 4.0% Due 2014 [Member]	Mar. 31, 2012 Convertible Senior Notes 4.0% Due 2014 [Member]	Dec. 31, 2011 Convertible Senior Notes 4.0% Due 2014 [Member]
Short-term Debt [Line Items]
Debt instrument, issuance date				May 16, 2008					April 24, 2009
Convertible senior notes issued				$ 550,000,000					$ 500,000,000
Equity component related to repurchases, convertible, effective interest rate				1.875%	1.875%	1.875%		1.875%		4.00%
Interest payable dates					May 1 and November 1				April 1 and October 1
Debt instrument, maturity date				May 01, 2013					Oct. 01, 2014
Convertible senior notes effective interest rate, maximum						9.40%				13.00%
Conversion rate, in shares				$ 24.1196					$ 32.9164
Common stock principal amount				1,000	1,000				1,000
Per share conversion price				$ 41.46	$ 41.46				$ 30.38
Conversion premium				20.00%					22.50%
Last reported selling price				$ 34.55					$ 24.80
Initial strike price of warrants				$ 41.46						$ 30.38
Upper strike price of warrants				$ 67.37						$ 44.64
Convertible notes conversion criteria associated with common stock trading price	the last reported sale price of the Company's Class A common stock for at least 20 trading days in the 30 consecutive trading day period ending on the last trading day of the preceding calendar quarter is more than 130% of the applicable conversion price per share of Class A common stock on the last day of such preceding calendar quarter
Convertible notes conversion criteria associated with common stock and convertible notes trading price	trading price per $1,000 principal amount of the Notes for each day in the measurement period was less than 95% of the product of the last reported sale price of Class A common stock
Terminated convertible note hedge transaction			55.00%
Common stock shares issuable	115,974,000	109,675,000	13,265,780
Carrying amount of the equity component						156,600,000				169,000,000
Debt instrument, principal balance						535,000,000	535,000,000			500,000,000	500,000,000
Debt discount						(41,117,000)	(50,030,000)			(94,498,000)	(102,388,000)
Carrying value						$ 493,883,000	$ 484,970,000			$ 405,502,000	$ 397,612,000