Financial Instruments and Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Debt (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	$ 11,232,129	$ 9,412,631
Fair Value of Debt	11,560,591	9,955,795
Credit Facilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	235,822	317,392
Fair Value of Debt	236,013	317,496
Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	8,353,096	6,067,277
Fair Value of Debt	8,681,755	6,537,100
Term Loans And Other Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	1,778,393	2,060,491
Fair Value of Debt	1,792,786	2,075,002
Secured Mortgages [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	864,818	967,471
Fair Value of Debt	$ 850,037	$ 1,026,197