Supplemental Cash Flow Information - Supplemental Cash Flow Information (Detail) - USD ($) $ in Thousands	6 Months Ended			12 Months Ended
	Jun. 30, 2018		Jun. 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	(103,439)		(84,653)
Non-cash investing and financing activities included:
Increase in asset retirement costs capitalized	19,561	[1]	3,855	$ 20,245
(Decrease) increase in accrued capital expenditures	$ (102,809)		$ 36,926

[1] Includes costs incurred whether capitalized or expensed.