Capitalized Costs and Accumulated Depreciation, Depletion and Amortization (Detail) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Natural gas and oil properties:
Properties subject to depletion	[1]	$ 11,193,577	$ 10,974,929
Unproved properties	[1]	2,106,568	2,110,277
Total	[1]	13,300,145	13,085,206
Accumulated depletion and depreciation	[1]	(4,194,876)	(4,062,021)
Natural gas and oil properties, successful efforts method, net	[1]	$ 9,105,269	$ 9,023,185

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