Financial Instruments and Fair Value Measurements - Fair Value of Debt (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Debt:
Carrying Value of Debt	$ 8,417,310	$ 11,790,794
Fair Value of Debt	9,184,920	12,719,075
Credit Facilities [Member]
Debt:
Carrying Value of Debt	630,836	888,966
Fair Value of Debt	633,796	893,577
Senior Notes [Member]
Debt:
Carrying Value of Debt	4,436,785	5,223,136
Fair Value of Debt	4,916,105	5,867,124
Exchangeable senior notes [Member]
Debt:
Carrying Value of Debt	397,481	876,884
Fair Value of Debt	535,066	1,007,236
Secured mortgage debt [Member]
Debt:
Carrying Value of Debt	1,974,909	3,625,908
Fair Value of Debt	2,115,313	3,765,556
Secured mortgage debt of consolidated entities [Member]
Debt:
Carrying Value of Debt	308,204	450,923
Fair Value of Debt	312,707	455,880
Other debt of consolidated entities [Member]
Debt:
Carrying Value of Debt	14,437	67,749
Fair Value of Debt	14,432	68,751
Other debt [Member]
Debt:
Carrying Value of Debt	654,658	657,228
Fair Value of Debt	$ 657,501	$ 660,951