Financial Instruments and Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Debt (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	$ 10,968,320	$ 11,089,815
Fair Value of Debt	11,678,449	11,453,129
Credit Facilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	112,906	50,500
Fair Value of Debt	112,906	50,513
Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	8,375,716	8,304,147
Fair Value of Debt	9,030,466	8,606,864
Term Loans and Unsecured Other [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	1,891,032	1,921,428
Fair Value of Debt	1,908,643	1,946,335
Secured Mortgages [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	588,666	813,740
Fair Value of Debt	$ 626,434	$ 849,417