Capitalized Costs and Accumulated Depreciation, Depletion and Amortization (Detail) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Natural gas and oil properties:
Properties subject to depletion	[1]	$ 10,277,879	$ 10,974,929
Unproved properties	[1]	2,061,903	2,110,277
Total	[1]	12,339,782	13,085,206
Accumulated depletion and depreciation	[1]	(4,044,212)	(4,062,021)
Natural gas and oil properties, successful efforts method, net	[1]	$ 8,295,570	$ 9,023,185

[1] ^{Includes capitalized asset retirement costs and the associated accumulated amortization.}