Supplemental Cash Flow Information - Summary of Supplemental Cash Flow Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Information [Abstract]
Capital Expenditures Incurred but Not yet Paid	$ 302,800	$ 223,600
Supplemental cash flow information:
Cash paid for interest	281,058	316,116	$ 301,743
Cash paid for income taxes	2	2	30
Cash received for income tax refunds	257	174	61,403
Asset Retirement Obligation, Additions or Revisions	$ 14,685	$ (10,063)	$ 22,472