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, 2015	Dec. 31, 2014	Dec. 31, 2013
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	$ 18,433,034	$ 16,295,767	$ 11,180,357
Extensions, discoveries and improved recoveries, less related costs	1,091,283	5,516,528	6,613,665
Revisions of previous quantity estimates	(2,156,028)	(1,755,366)	(1,765,300)
Changes in estimated future development and abandonment costs	5,008,731	476,665	1,942,585
Sales of Minerals in Place	(7,768)	(3,196)
Purchases of minerals in place			12,012
Net change in prices and production costs	(16,111,142)	(1,925,349)	263,541
Accretion of discount	1,843,303	1,629,576	1,118,036
Sales of crude oil and natural gas produced, net of production costs	(2,002,997)	(3,500,790)	(2,992,447)
Development costs incurred during the period	1,394,584	2,466,748	1,210,223
Change in timing of estimated future production and other	(3,844,259)	(309,902)	464,111
Change in income taxes	2,827,543	(457,647)	(1,751,016)
Net change	(11,956,750)	2,137,267	5,115,410
Standardized measure of discounted future net cash flows at end of year	$ 6,476,284	$ 18,433,034	$ 16,295,767