Debt (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Short and Long Term Debt [Line Items]
Amount Outstanding	$ 11,382,408	$ 6,506,029
Weighted Average Interest Rate	5.12%	5.79%
Credit Facilities [Member]
Short and Long Term Debt [Line Items]
Amount Outstanding	936,796	520,141
Weighted Average Interest Rate	2.17%	3.53%
Senior Debt [Member]
Short and Long Term Debt [Line Items]
Amount Outstanding	4,772,607	3,195,724
Weighted Average Interest Rate	6.30%	6.63%
Exchangeable senior notes [Member]
Short and Long Term Debt [Line Items]
Amount Outstanding	1,315,448	1,521,568
Weighted Average Interest Rate	4.82%	4.90%
Secured mortgage debt [Member]
Short and Long Term Debt [Line Items]
Amount Outstanding	1,725,773	1,249,729
Weighted Average Interest Rate	4.71%	5.67%
Secured mortgage debt of consolidated investees [Member]
Short and Long Term Debt [Line Items]
Amount Outstanding	1,468,637
Weighted Average Interest Rate	4.54%
Other debt of consolidated investees [Member]
Short and Long Term Debt [Line Items]
Amount Outstanding	775,763
Weighted Average Interest Rate	5.30%
Other debt [Member]
Short and Long Term Debt [Line Items]
Amount Outstanding	$ 387,384	$ 18,867
Weighted Average Interest Rate	2.44%	6.48%