Supplemental Information on Natural Gas and Oil Exploration, Development and Production Activities (Unaudited) - Capitalized Costs and Accumulated Depreciation, Depletion and Amortization (Detail) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Natural gas and oil properties:
Properties subject to depletion	[1]	$ 9,345,557	$ 10,974,929	$ 10,572,453
Unproved properties	[1]	868,180	2,110,277	2,644,000
Total	[1]	10,213,737	13,085,206	13,216,453
Accumulated depreciation, depletion and amortization	[1]	(4,172,702)	(4,062,021)	(3,649,716)
Natural gas and oil properties, successful efforts method, net	[1]	$ 6,041,035	$ 9,023,185	$ 9,566,737

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