Supplemental Information on Natural Gas and Oil Exploration, Development and Production Activities (Unaudited) - Standardized Measure of Discounted Future Net Cash Flows (Detail) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Extractive Industries [Abstract]
Future cash inflows		$ 64,287,737	$ 43,500,054
Future costs:
Production		(25,626,373)	(18,958,695)
Development	[1]	(3,824,936)	(3,072,688)
Future net cash flows before income taxes		34,836,428	21,468,671
Future income tax expense		(7,285,274)	(3,989,459)
Total future net cash flows before 10% discount		27,551,154	17,479,212
10% annual discount		(16,435,560)	(10,313,998)
Standardized measure of discounted future net cash flows		$ 11,115,594	$ 7,165,214	$ 3,451,929	$ 2,725,863

[1] 2018 includes $494.5 million of undiscounted future asset retirement costs estimated as of December 31, 2018, using current estimates of future abandonment costs.