Supplemental Cash Flow Information - Supplemental Cash Flow Information (Detail) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Mar. 31, 2018		Mar. 31, 2017	Dec. 31, 2017	[1]
Net cash provided from operating activities included:
Income taxes refunded from taxing authorities	$ 7,518
Interest paid	(57,536)		$ (43,864)
Non-cash investing and financing activities included:
Increase in asset retirement costs capitalized	5,063	[1]	1,715	$ 20,245
(Decrease) increase in accrued capital expenditures	$ (77,365)		$ 39,569

[1] Includes costs incurred whether capitalized or expensed.