Debt (Schedule of Debt Retirement) (Details) (USD $) In Thousands, unless otherwise specified	1 Months Ended				2 Months Ended		12 Months Ended			36 Months Ended	1 Months Ended	2 Months Ended		1 Months Ended	2 Months Ended		1 Months Ended	2 Months Ended	1 Months Ended												2 Months Ended	1 Months Ended					2 Months Ended	1 Months Ended
	Jun. 30, 2011	Dec. 31, 2010	Oct. 31, 2010	Sep. 30, 2009	Dec. 31, 2011	Jun. 30, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011	Oct. 31, 2010 Unsecured Senior Notes 5.25% Due January 2014 [Member]	Dec. 31, 2011 Unsecured Senior Notes 5.25% Due January 2014 [Member]	Jun. 30, 2009 Unsecured Senior Notes 5.25% Due January 2014 [Member]	Oct. 31, 2010 Unsecured Senior Notes 5.20% Due February 2015 [Member]	Dec. 31, 2011 Unsecured Senior Notes 5.20% Due February 2015 [Member]	Jun. 30, 2009 Unsecured Senior Notes 5.20% Due February 2015 [Member]	Oct. 31, 2010 Unsecured Senior Notes 5.25% Due June 2015 [Member]	Dec. 31, 2011 Unsecured Senior Notes 5.25% Due June 2015 [Member]	Jun. 30, 2011 Unsecured Senior Notes 5.45% Due August 2012 [Member]	Nov. 30, 2010 Unsecured Senior Notes 5.45% Due August 2012 [Member]	Sep. 30, 2009 Unsecured Senior Notes 5.45% Due August 2012 [Member]	Jun. 30, 2011 Unsecured Senior Notes 5.125% Due October 2013 [Member]	Oct. 31, 2010 Unsecured Senior Notes 5.125% Due October 2013 [Member]	Sep. 30, 2009 Unsecured Senior Notes 5.125% Due October 2013 [Member]	Feb. 28, 2011 Unsecured Senior Notes 8.125% Due February 2011 [Member]	Sep. 30, 2009 Unsecured Senior Notes 8.125% Due February 2011 [Member]	Dec. 31, 2010 Unsecured senior notes 7.875% due Feb 2011 [Member]	Sep. 30, 2009 Unsecured senior notes 7.875% due Feb 2011 [Member]	Dec. 31, 2010 Unsecured Senior Notes 7.875% due July 2011 [Member]	Sep. 30, 2009 Unsecured Senior Notes 7.875% due July 2011 [Member]	Jun. 30, 2009 Unsecured Senior Notes 7.875% due July 2011 [Member]	Dec. 31, 2010 Unsecured Senior Notes 7.50% due January 2012 [Member]	Sep. 30, 2009 Unsecured Senior Notes 7.50% due January 2012 [Member]	Oct. 31, 2010 Unsecured Senior Notes 4.55% due November 2010 [Member]	Sep. 30, 2009 Unsecured Senior Notes 4.55% due November 2010 [Member]	Oct. 31, 2010 Unsecured Senior Notes 6.25% Due February 2013 [Member]	Jun. 30, 2009 Unsecured Senior Notes 6.25% Due February 2013 [Member]	Oct. 31, 2010 Unsecured Senior Notes 5.70% Due May 2014 [Member]	Sep. 30, 2009 Unsecured Senior Notes 5.80% due September 2009 [Member]	Jul. 31, 2009 Unsecured Senior Notes 4.875% due July 2009 [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount	$ 52,996	$ 328,043	$ 500,000	$ 1,500,000	$ 257,000	$ 192,924	$ 323,896	$ 898,470	$ 1,929,257	$ 3,151,623	$ 128,077	$ 80,000	$ 36,004	$ 47,838	$ 37,000	$ 57,135	$ 25,536	$ 140,000	$ 7,306	$ 23,000	$ 168,301	$ 45,690	$ 104,749	$ 30,084	$ 13,900	$ 186,098	$ 85,595	$ 306,905	$ 132,186	$ 341,377	$ 25,000	$ 110,262	$ 214,662	$ 47,427	$ 252,573	$ 162,471	$ 74,785	$ 31,329	$ 210,920	$ 25,413
Debt Instrument, Interest Rate, Stated Percentage											5.25%	5.25%	5.25%	5.20%	5.20%	5.20%	5.25%	5.25%	5.45%	5.45%	5.45%	5.125%	5.125%	5.125%	8.125%	8.125%	7.875%	7.875%	7.875%	7.875%	7.875%	7.50%	7.50%	4.55%	4.55%	6.25%	6.25%	5.70%	5.80%	4.875%
Debt Instrument, Maturity Date, Description											January 2014	January 2014	January 2014	February 2015	February 2015	February 2015	June 2015	June 2015	August 2012	August 2012	August 2012	October 2013	October 2013	October 2013	February 2011	February 2011	February 2011	February 2011	July 2011	July 2011	July 2011	January 2012	January 2012	November 2010	November 2010	February 2013	February 2013	May 2014	September 2009	July 2009