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, 2018	Dec. 31, 2017	Dec. 31, 2016
Natural gas and oil properties:
Properties subject to depletion	[1]	$ 10,974,929	$ 10,572,453	$ 9,462,350
Unproved properties	[1]	2,110,277	2,644,000	2,923,803
Total	[1]	13,085,206	13,216,453	12,386,153
Accumulated depletion and depreciation	[1]	(4,062,021)	(3,649,716)	(3,129,816)
Natural gas and oil properties, successful efforts method, net	[1]	$ 9,023,185	$ 9,566,737	$ 9,256,337

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