Financial Instruments and Fair Value Measurements - Fair Value of Debt (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Debt:
Carrying Value of Debt	$ 9,074,123	$ 11,790,794
Fair Value of Debt	10,040,168	12,719,075
Credit Facilities [Member]
Debt:
Carrying Value of Debt	421,248	888,966
Fair Value of Debt	422,516	893,577
Senior Notes [Member]
Debt:
Carrying Value of Debt	4,992,836	5,223,136
Fair Value of Debt	5,635,078	5,867,124
Exchangeable Senior Notes [Member]
Debt:
Carrying Value of Debt	738,066	876,884
Fair Value of Debt	874,884	1,007,236
Secured Mortgage Debt [Member]
Debt:
Carrying Value of Debt	1,875,502	3,625,908
Fair Value of Debt	2,047,601	3,765,556
Secured Mortgage Debt of Consolidated Entities [Member]
Debt:
Carrying Value of Debt	438,915	450,923
Fair Value of Debt	447,605	455,880
Other Debt of Consolidated Entities [Member]
Debt:
Carrying Value of Debt	64,392	67,749
Fair Value of Debt	65,944	68,751
Other Debt [Member]
Debt:
Carrying Value of Debt	543,164	657,228
Fair Value of Debt	$ 546,540	$ 660,951