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, 2018	Dec. 31, 2017	Dec. 31, 2016
Revisions of previous estimates
Changes in prices and production costs	$ 2,959,488	$ 2,615,825	$ (212,867)
Revisions in quantities	667,763	445,667	96,615
Changes in future development and abandonment costs	(557,518)	(497,400)	(314,864)
Net change in income taxes	(1,075,867)	(706,531)	27,842
Accretion of discount	814,725	372,743	302,920
Purchases of reserves in place		6,173	488,959
Additions to proved reserves from extensions, discoveries and improved recovery	2,543,296	2,128,135	541,095
Natural gas, NGLs and oil sales, net of production costs	(1,547,580)	(1,237,970)	(509,174)
Development costs incurred during the period	722,074	885,803	435,928
Sales of reserves in place	(226,953)	(32,946)	(65,538)
Timing and other	(349,048)	(266,214)	(64,850)
Net change for the year	3,950,380	3,713,285	726,066
Beginning of year	7,165,214	3,451,929	2,725,863
End of year	$ 11,115,594	$ 7,165,214	$ 3,451,929