Summary of Significant Accounting Policies - Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Asset retirement obligations
Asset retirement obligation as of beginning of period	$ 461,821	$ 287,805
Accretion expense	22,506	13,733
Liabilities incurred	10,293	8,985
Liabilities settled	(4,030)	(3,569)
Liabilities assumed in acquisitions	45,825	0
Liabilities removed due to divestitures	(54,836)	(5,535)
Change in estimates	41,978	160,402
Asset retirement obligation as of end of period	$ 523,557	$ 461,821