Financial Instruments and Fair Value Measurements - Fair Value of Debt (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Debt:
Carrying Value of Debt	$ 9,119,317	$ 11,790,794
Fair Value of Debt	9,850,847	12,719,075
Credit Facilities [Member]
Debt:
Carrying Value of Debt	992,776	888,966
Fair Value of Debt	993,310	893,577
Senior notes [Member]
Debt:
Carrying Value of Debt	4,980,625	5,223,136
Fair Value of Debt	5,415,442	5,867,124
Exchangeable senior notes [Member]
Debt:
Carrying Value of Debt	397,481	876,884
Fair Value of Debt	525,958	1,007,236
Secured mortgage debt [Member]
Debt:
Carrying Value of Debt	1,772,342	3,625,908
Fair Value of Debt	1,922,436	3,765,556
Secured mortgage debt of consolidated entities [Member]
Debt:
Carrying Value of Debt	296,783	450,923
Fair Value of Debt	304,063	455,880
Other debt of consolidated entities [Member]
Debt:
Carrying Value of Debt	4,345	67,749
Fair Value of Debt	4,345	68,751
Other Debt [Member]
Debt:
Carrying Value of Debt	674,965	657,228
Fair Value of Debt	$ 685,293	$ 660,951