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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, 2020
Dec. 31, 2019
Dec. 31, 2018
Natural gas and oil properties:      
Properties subject to depletion [1] $ 8,891,348 $ 9,345,557 $ 10,974,929
Unproved properties [1] 859,766 868,180 2,110,277
Total [1] 9,751,114 10,213,737 13,085,206
Accumulated depreciation, depletion and amortization (4,064,305) (4,172,702) [1] (4,062,021) [1]
Natural gas and oil properties, successful efforts method, net [1] $ 5,686,809 $ 6,041,035 $ 9,023,185
[1] Includes capitalized asset retirement costs and the associated accumulated amortization.