Natural Gas Producing Activities (Unaudited) - Summary of Changes in the Standardized Measure of Discounted Net Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Roll Forward]
Net sales and transfers of natural gas and oil produced	$ (784,163)	$ (1,884,877)	$ (2,802,742)
Net changes in prices, production and development costs	(6,761,447)	(3,502,434)	2,949,606
Extensions, discoveries and improved recovery, net of related costs	714,808	870,504	1,616,653
Development costs incurred	797,796	1,002,389	1,630,506
Net purchase of minerals in place	350,075	0	0
Net sale of minerals in place	(226,497)	0	(849,162)
Revisions of previous quantity estimates	(324,415)	(2,080,040)	(811,576)
Accretion of discount	849,267	900,004	834,026
Net change in income taxes	152,978	1,444,368	(289,549)
Timing and other	105,383	130,861	332,202
Net (decrease) increase	(5,126,215)	(3,119,225)	2,609,964
Balance at January 1	8,492,673	11,611,898	9,001,934
Balance at December 31	$ 3,366,458	$ 8,492,673	$ 11,611,898