Debt - Debt Summary (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Debt	$ 11,626,831	$ 9,336,977
Credit Facilities [Member]
Debt Instrument [Line Items]
Debt	0	0
Senior Notes [Member]
Debt Instrument [Line Items]
Debt	6,516,392	6,046,965
Exchangeable Senior Notes [Member]
Debt Instrument [Line Items]
Debt	0	456,373
Term Loan [Member]
Debt Instrument [Line Items]
Debt	2,100,000
Secured Mortgage Debt [Member]
Debt Instrument [Line Items]
Debt	$ 1,172,473	$ 1,042,628
Debts Of Operating Partnership [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.20%	3.70%
Debt	$ 11,626,831	$ 9,336,977
Debts Of Operating Partnership [Member] | Credit Facilities [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	0.00%	0.00%
Debt	$ 0	$ 0
Debts Of Operating Partnership [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.30%	3.70%
Debt	$ 6,516,392	$ 6,046,965
Debts Of Operating Partnership [Member] | Exchangeable Senior Notes [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	0.00%	3.70%
Debt	$ 0	$ 456,373
Debts Of Operating Partnership [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	2.10%	1.40%
Debt	$ 2,100,009	$ 568,037
Debts Of Operating Partnership [Member] | Other Debt [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	6.20%	6.20%
Debt	$ 15,448	$ 16,087
Debts Of Operating Partnership [Member] | Secured Mortgage Debt [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	5.10%	6.10%
Debt	$ 1,172,473	$ 1,042,628
Debts Of Operating Partnership [Member] | Secured Mortgage Debt of Consolidated Entities [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	2.90%	2.50%
Debt	$ 1,822,509	$ 1,206,887