Capitalized Costs and Accumulated Depreciation, Depletion and Amortization (Detail) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019
Natural gas properties:
Properties subject to depletion	[1]	$ 8,784,788	$ 9,345,557
Unproved properties	[1]	862,113	868,180
Total	[1]	9,646,901	10,213,737
Accumulated depletion and depreciation	[1]	(3,975,930)	(4,172,702)
Natural gas and oil properties, successful efforts method, net	[1]	$ 5,670,971	$ 6,041,035

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