Supplemental Information on Natural Gas and Oil Exploration, Development and Production Activities (Unaudited) - Changes in Discounted Future Net Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revisions of previous estimates
Changes in prices and production costs	$ (7,231,629)	$ 5,069	$ 2,172,704
Revisions in quantities	(868,886)	102,760	513,168
Changes in future development and abandonment costs	359,540	(407,688)	(275,468)
Net change in income taxes	2,173,904	(441,935)	(1,299,227)
Accretion of discount	1,007,027	789,754	395,989
Purchases of reserves in place	0	297,358	0
Additions to proved reserves from extensions, discoveries and improved recovery	486,478	2,713,999	1,981,054
Natural gas, NGLs and oil sales, net of production costs	(522,682)	(1,391,663)	(1,286,103)
Development costs incurred during the period	1,033,539	755,384	462,862
Sales of reserves in place	(1,050,237)	(249,055)	(162,463)
Timing and other	(254,218)	(443,187)	135,910
Net change for the year	(4,867,164)	1,730,796	2,638,426
Beginning of year	7,593,027	5,862,231	3,223,805
End of year	$ 2,725,863	$ 7,593,027	$ 5,862,231