Supplemental Information on Natural Gas and Oil Exploration, Development and Production Activities (Unaudited) - Changes in Proved Undeveloped Reserves (Detail)	12 Months Ended
	Dec. 31, 2015 MMcfe
Extractive Industries [Abstract]
Beginning proved undeveloped reserves at December 31, 2014	4,960,468
Undeveloped reserves transferred to developed	(762,936)
Revisions	(441,874)	[1]
Purchases/(sales)	(201,809)
Extension and discoveries	915,739
Ending proved undeveloped reserves at December 31, 2015	4,469,588

[1] Includes 1.2 Tcfe of proved undeveloped reserves dropped due to the five year rule which can be included in our future proved reserves as these locations are added back to our five-year development plan.