Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Asset retirement obligation	$ 9,809	$ 91
Revision of estimated cash flows	(1,042)	5,471
MLMC
Segment Reporting Information [Line Items]
Asset retirement obligation	9,800
Asset capitalized as a component of property, plant and equipment, net	9,800
Revision of estimated cash flows		3,100
Bellaire
Segment Reporting Information [Line Items]
Fair value of trust assets	11,100	10,100
Centennial
Segment Reporting Information [Line Items]
Increase (decrease) in asset retirement obligation	4,800	5,400
Escrow account	3,800	2,400
Settlement receivable from third parties	1,400
Other long-term liabilities, contingent and noncontingent guarantee liabilities	2,400
Company transferred		3,400
Net loss on the transactions		400
Revision of estimated cash flows		$ 2,000
Centennial | Surety Bond
Segment Reporting Information [Line Items]
Surety bonds outstanding	$ 5,800