Debt - Debt Summary (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Weighted Average Interest Rate	2.90%	2.90%
Debt	$ 9,427,124	$ 9,412,631
Credit Facilities [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	0.90%	1.80%
Debt	$ 11,658	$ 317,392
Senior Notes [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	2.90%	3.00%
Debt	$ 7,102,381	$ 6,067,277
Term Loan [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	1.20%	1.70%
Debt	$ 1,402,568	$ 2,046,945
Unsecured Other Debt [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	6.10%	6.10%
Debt	$ 13,093	$ 13,546
Secured Mortgages [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	5.50%	5.30%
Debt	$ 897,424	$ 967,471