Debt - Debt Summary (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Weighted Average Interest Rate	2.70%	2.90%
Debt	$ 11,089,815	$ 9,412,631
Credit Facilities [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	3.40%	1.80%
Debt	$ 50,500	$ 317,392
Senior Notes [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	2.70%	3.00%
Debt	$ 8,304,147	$ 6,067,277
Term Loans and Unsecured Other [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	1.80%	1.70%
Debt	$ 1,921,428	$ 2,060,491
Secured Mortgage [Member]
Debt Instrument [Line Items]
Weighted Average Interest Rate	5.10%	5.30%
Debt	$ 813,740	$ 967,471