Debt (Narrative) (Details) (USD $)	0 Months Ended	3 Months Ended			6 Months Ended			6 Months Ended	0 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended		12 Months Ended	6 Months Ended		12 Months Ended	6 Months Ended		12 Months Ended
	Jun. 15, 2011	Jun. 30, 2011	Jun. 30, 2010	Sep. 30, 2009	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010	Jun. 30, 2011 Investment And Other Income (Expense) [Member]	Jun. 01, 2011 7.25% Senior Notes Due May 15, 2018 [Member]	Jun. 30, 2011 7.25% Senior Notes Due May 15, 2018 [Member]	Dec. 31, 2010 7.25% Senior Notes Due May 15, 2018 [Member]	Jun. 30, 2011 11.25% Senior Notes Due February 1, 2019 [Member]	Jun. 30, 2010 11.25% Senior Notes Due February 1, 2019 [Member]	Dec. 31, 2010 11.25% Senior Notes Due February 1, 2019 [Member]	Jun. 30, 2011 6.125% Senior Notes Due January 15, 2017 [Member]	Jun. 30, 2010 6.125% Senior Notes Due January 15, 2017 [Member]	Dec. 31, 2010 6.125% Senior Notes Due January 15, 2017 [Member]	Jun. 30, 2011 5.50% Senior Notes Due May 15, 2015 [Member]	Jun. 30, 2010 5.50% Senior Notes Due May 15, 2015 [Member]	Dec. 31, 2010 5.50% Senior Notes Due May 15, 2015 [Member]
Amount of difference between fair value and book value		$ 78,800,000			$ 78,800,000		$ 259,300,000
Debt instrument face amount									600,000,000
Interest rate	5.50%			4.95%					7.25%	7.25%	7.25%	11.25%		11.25%	6.125%		6.125%	5.50%		5.50%
Maturity date	May 15, 2015			May 15, 2010						May 15, 2018	May 15, 2018	Feb. 01, 2019	Feb. 01, 2019	Feb. 01, 2019	Jan. 15, 2017	Jan. 15, 2017	Jan. 15, 2017	May 15, 2015	May 15, 2015	May 15, 2015
Interest rate terms									Interest on the notes is payable semi-annually on May 15 and November 15 of each year, commencing on November 15, 2011.
Repurchase of debt	100,000,000			174,200,000								216,200,000			100,000,000			100,000,000
Loss on debt extinguishment					68,600,000			(68,600,000)
Interest income		$ 3,600,000	$ 1,700,000		$ 6,200,000	$ 3,600,000