Supplemental Cash Flow Information - Supplemental Cash Flow Information (Detail) - USD ($) $ in Thousands	9 Months Ended			12 Months Ended
	Sep. 30, 2018		Sep. 30, 2017	Dec. 31, 2017	[1]
Net cash provided from operating activities included:
Income taxes refunded (paid) to taxing authorities	$ 7,521		$ (98)
Interest paid	(161,444)		(136,863)
Non-cash investing and financing activities included:
Increase in asset retirement costs capitalized	20,452	[1]	6,460	$ 20,245
(Decrease) increase in accrued capital expenditures	$ (107,070)		$ 52,289

[1] Includes costs incurred whether capitalized or expensed.