Natural Gas Producing Activities (Unaudited) - Estimated Future Net Cash Flows from Natural Gas and Oil Reserves (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Extractive Industries [Abstract]
Future cash inflows	$ 42,499,686	$ 60,603,624	$ 51,423,920
Future production costs	(19,114,076)	(20,463,567)	(18,379,892)
Future development costs	(2,617,731)	(5,854,503)	(5,637,676)
Future income tax expenses	(3,013,667)	(6,823,621)	(5,811,125)
Future net cash flow	17,754,212	27,461,933	21,595,227
10% annual discount for estimated timing of cash flows	(9,261,539)	(15,850,035)	(12,593,293)
Standardized measure of discounted future net cash flows	$ 8,492,673	$ 11,611,898	$ 9,001,934	$ 988,754