Debt - Debt Summary (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Schedule of Capitalization, Long-term Debt [Line Items]
Weighted Average Interest Rate	3.60%	4.20%
Amount Outstanding	$ 8,822,952	$ 9,011,216
Credit Facilities [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Weighted Average Interest Rate	1.10%	1.20%
Amount Outstanding	741,610	725,483
Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Weighted Average Interest Rate	3.90%	4.50%
Amount Outstanding	5,443,138	5,357,933
Exchangeable Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Weighted Average Interest Rate	3.30%	3.30%
Amount Outstanding	451,999	438,481
Secured Mortgage Debt [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Weighted Average Interest Rate	5.90%	5.60%
Amount Outstanding	1,141,772	1,696,597
Secured Mortgage Debt of Consolidated Entities [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Weighted Average Interest Rate	3.90%	4.70%
Amount Outstanding	26,064	239,992
Term Loans [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Weighted Average Interest Rate	1.10%	1.70%
Amount Outstanding	1,001,930	535,908
Other Debt [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Weighted Average Interest Rate	6.20%	6.20%
Amount Outstanding	$ 16,439	$ 16,822