Supplemental Cash Flow Information - Supplemental Cash Flow Information (Detail) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Mar. 31, 2019		Mar. 31, 2018	Dec. 31, 2018	[1]
Net cash provided from operating activities included:
Income taxes refunded from taxing authorities			$ 7,518
Interest paid	$ (54,632)		(57,536)
Non-cash investing and financing activities included:
Increase in asset retirement costs capitalized	1,532	[1]	5,063	$ 28,826
Increase (decrease) in accrued capital expenditures	$ 22,764		$ (77,365)

[1] Includes costs incurred whether capitalized or expensed.