Exchangeable Senior Notes (Narrative) (Details) (USD $)	0 Months Ended		12 Months Ended			0 Months Ended			3 Months Ended
	Dec. 21, 2011	Nov. 01, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 21, 2011 Senior Notes [Member]	Nov. 01, 2011 Senior Notes [Member]	Nov. 01, 2011 Senior Notes [Member]	Dec. 31, 2008 Senior Notes [Member]	Dec. 31, 2011 Senior Notes [Member]	Oct. 31, 2006 Senior Notes [Member]
Debt Instrument [Line Items]
Senior notes, principal amount			$ 2,663,336,000	$ 2,618,932,000							$ 200,000,000
Unsecured term loan borrowed facility			135,000,000			5,000,000	135,000,000
Amount of accrued interest						29,000		2,784,000
Coupon rate											4.125%
Repurchased senior notes, principal									60,000,000
Out standing principal amount				$ 140,000,000					$ 140,000,000	$ 0
Initial exchange price of senior notes									$ 73.34
Conversion price per share, as adjusted	$ 72.87	$ 72.87		$ 72.87	$ 72.87
Debt instrument maturity date			November 1, 2026
Effective interest rate			5.75%	5.75%	5.75%