Debt - Debt Summary (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Short And Long Term Debt [Line Items]
Weighted Average Interest Rate	4.70%	4.40%
Amount Outstanding	$ 8,417,310	$ 11,790,794
Credit Facilities [Member]
Short And Long Term Debt [Line Items]
Weighted Average Interest Rate	1.60%	1.50%
Amount Outstanding	630,836	888,966
Senior Notes [Member]
Short And Long Term Debt [Line Items]
Weighted Average Interest Rate	5.60%	5.60%
Amount Outstanding	4,436,785	5,223,136
Exchangeable senior notes [Member]
Short And Long Term Debt [Line Items]
Weighted Average Interest Rate	3.30%	4.60%
Amount Outstanding	397,481	876,884
Secured mortgage debt [Member]
Short And Long Term Debt [Line Items]
Weighted Average Interest Rate	5.10%	4.00%
Amount Outstanding	1,974,909	3,625,908
Secured mortgage debt of consolidated entities [Member]
Short And Long Term Debt [Line Items]
Weighted Average Interest Rate	4.50%	4.40%
Amount Outstanding	308,204	450,923
Other debt of consolidated entities [Member]
Short And Long Term Debt [Line Items]
Weighted Average Interest Rate	4.80%	4.80%
Amount Outstanding	14,437	67,749
Other debt [Member]
Short And Long Term Debt [Line Items]
Weighted Average Interest Rate	1.80%	1.80%
Amount Outstanding	$ 654,658	$ 657,228