Supplemental Information on Oil and Natural Gas Operations - Unaudited - Summary of Standardized Measure of Discounted Future Net Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Extractive Industries [Abstract]
Future cash inflows				$ 1,921,329	$ 6,635,751	$ 7,040,928
Future production costs				(651,396)	(2,413,004)	(2,062,657)
Future development costs				(679,355)	(1,511,687)	(1,431,101)
Future income taxes				0	(609,516)	(884,637)
Future net cash flows				590,578	2,101,544	2,662,533
10% annual discount				13,259	(682,752)	(977,531)
Standardized measure of discounted future net cash flows	$ 1,418,792	$ 1,685,002	$ 1,513,859	$ 603,837	$ 1,418,792	$ 1,685,002
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]
Standardized measure at beginning of year	1,418,792	1,685,002	1,513,859
Sales and transfers of oil, gas and NGLs produced, net of production costs	(340,477)	(486,232)	(708,017)
Changes in price, net of future production costs	(237,747)	(864,118)	229,425
Extensions and discoveries, net of future production and development costs	1,573	549,649	155,592
Changes in estimated future development costs, net of development costs incurred during the period	731,115	203,026	28,684
Revisions of quantity estimates	(1,458,652)	(27,495)	281,558
Accretion of discount	174,456	222,009	202,087
Net change in income taxes	325,768	209,323	(28,084)
Purchases of reserves in-place	3,493	0	0
Sales of reserves in-place	0	(152,787)	15,531
Changes in production rates due to timing and other	(14,484)	80,415	(5,633)
Net increase (decrease) in standardized measure	(814,955)	(266,210)	171,143
Standardized measure at end of year	$ 603,837	$ 1,418,792	$ 1,685,002