Supplemental Crude Oil and Natural Gas Information - Changes in Standardized Measure of Discounted Future Net Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]
Standardized measure of discounted future net cash flows at beginning of year	$ 6,476,284	$ 18,433,034	$ 16,295,767
Extensions, discoveries and improved recoveries, less related costs	786,587	1,091,283	5,516,528
Revisions of previous quantity estimates	(794,785)	(2,156,028)	(1,755,366)
Changes in estimated future development and abandonment costs	1,651,218	5,008,731	476,665
Sales of Minerals in Place	(90,390)	(7,768)
Purchases of minerals in place			(3,196)
Net change in prices and production costs	(2,003,163)	(16,111,142)	(1,925,349)
Accretion of discount	798,597	1,843,303	1,629,576
Sales of crude oil and natural gas produced, net of production costs	(1,595,281)	(2,002,997)	(3,500,790)
Development costs incurred during the period	454,983	1,394,584	2,466,748
Change in timing of estimated future production and other	(538,665)	(3,844,259)	(309,902)
Change in income taxes	364,838	2,827,543	(457,647)
Net change	(966,061)	(11,956,750)	2,137,267
Standardized measure of discounted future net cash flows at end of year	$ 5,510,223	$ 6,476,284	$ 18,433,034