Debt - Debt Summary (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Weighted Average Interest Rate	2.90%	3.20%
Debt	$ 9,412,631	$ 10,608,294
Credit Facilities [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	1.80%	1.00%
Debt	$ 317,392	$ 35,023
Senior Notes [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.00%	3.30%
Debt	$ 6,067,277	$ 6,417,492
Term Loan [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	1.70%	1.40%
Debt	$ 2,046,945	$ 1,484,523
Unsecured Other Debt [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	6.10%	6.10%
Debt	$ 13,546	$ 14,478
Secured Mortgages [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	5.70%	4.90%
Debt	$ 808,096	$ 979,585
Secured Mortgage Debt of Consolidated Entities [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	2.90%	3.00%
Debt	$ 159,375	$ 1,677,193