Accounting Policies (Details 2) (USD $)	3 Months Ended								12 Months Ended					1 Months Ended						12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2011 Nonconvertible debt	Nov. 30, 2011 3 7/8 % Convertible Senior Notes due 2011 upon maturity	Dec. 31, 2011 3 7/8 % Convertible Senior Notes due 2011 upon maturity	Nov. 15, 2011 3 7/8 % Convertible Senior Notes due 2011 upon maturity	Dec. 31, 2010 3 7/8 % Convertible Senior Notes due 2011 upon maturity	Mar. 31, 2010 3 7/8 % Convertible Senior Notes due 2011 upon maturity	Dec. 31, 2008 Adoption of FASB guidance relating to convertible debt instruments that may be settled in cash upon conversion Nonconvertible debt	Dec. 31, 2011 Adjustment Adoption of FASB guidance relating to convertible debt instruments that may be settled in cash upon conversion	Dec. 31, 2010 Adjustment Adoption of FASB guidance relating to convertible debt instruments that may be settled in cash upon conversion	Dec. 31, 2009 Adjustment Adoption of FASB guidance relating to convertible debt instruments that may be settled in cash upon conversion	Dec. 31, 2008 Adjustment Adoption of FASB guidance relating to convertible debt instruments that may be settled in cash upon conversion
Accounting Policies
Borrowing rate (as a percent)													6.125%	3.875%	3.875%	3.875%	3.875%	3.875%
Real estate assets for which tenant purchase option is recorded, net	$ 644,000,000								$ 644,000,000
Decrease in net income on adoption of FASB guidance	(192,948,000)	(102,885,000)	(19,676,000)	(48,984,000)	(77,583,000)	(57,898,000)	(58,067,000)	(52,619,000)	(364,493,000)	(246,167,000)	(266,495,000)									4,000,000	4,200,000	3,900,000
Decrease in net income per diluted share on adoption of FASB guidance (in dollars per share)	$ (0.66)	$ (0.35)	$ (0.11)	$ (0.30)	$ (0.49)	$ (0.37)	$ (0.37)	$ (0.34)	$ (1.58)	$ (1.56)	$ (1.74)									$ 0.02	$ 0.03	$ 0.03
Increase in total equity on adoption of FASB guidance	9,355,944,000				2,390,205,000				9,355,944,000	2,390,205,000	2,484,060,000	2,179,735,000											12,100,000
Calculated equity component on adoption of FASB guidance																			19,500,000
Remaining unamortized liability component	6,429,116,000				2,900,044,000				6,429,116,000	2,900,044,000
Principal amount repaid														$ 230,000,000
Aggregate shares of common stock issued for the conversion value in excess of the principal amount														943,714