Investment in Laramie Energy, LLC - Narrative (Details) - USD ($)			3 Months Ended	12 Months Ended
	Oct. 18, 2018	Feb. 28, 2018	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Nov. 20, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Mar. 04, 2019	Dec. 31, 2017	Mar. 01, 2016
Schedule of Equity Method Investments [Line Items]
Investment in Laramie Energy, LLC			$ 46,905,000	$ 0	$ 46,905,000
Asset impairment loss				$ 85,806,000	0	$ 0
Laramie Energy Company
Schedule of Equity Method Investments [Line Items]
Ownership of Laramie Energy, LLC	46.00%	39.10%		46.00%									42.30%
Equity method investments, fair value									$ 1,900,000	$ 51,800,000
Equity method investment, aggregate cost									$ 47,200,000	$ 133,300,000
Impairment charge				$ 45,294,000	81,515,000	0
Investment in Laramie Energy, LLC			46,905,000		46,905,000	136,656,000		$ 0				$ 127,192,000
Asset impairment loss				0	355,220,000	$ 0
Laramie Energy Company
Schedule of Equity Method Investments [Line Items]
Asset impairment loss			355,200,000
Disposal group, property, plant and equipment											$ 17,500,000
Laramie Energy Company | Capital Unit, Class A
Schedule of Equity Method Investments [Line Items]
Stock repurchased during period (in shares)	138,795
Stock repurchased during period	$ 14,800,000
Unaffiliated Third Party | Laramie Energy Company
Schedule of Equity Method Investments [Line Items]
Equity method investments, fair value		$ 28,100,000
Investment in Laramie Energy, LLC		$ 20,000,000.0
Shares issued (in shares)		70,227
Additional payments to acquire equity method investments		$ 3,500,000
Revolving Credit Facility | Laramie Energy Company
Schedule of Equity Method Investments [Line Items]
Line credit maximum borrowing amount				400,000,000.0
Current borrowing capacity				139,700,000
Balance outstanding on the revolving credit facility			$ 201,200,000	139,700,000	$ 201,200,000
Revolving Credit Facility | Laramie Energy Company | Deficiency Loan
Schedule of Equity Method Investments [Line Items]
Line credit maximum borrowing amount							$ 140,000,000.0
Current borrowing capacity							$ 60,000,000.0
Balance outstanding on the revolving credit facility				$ 60,000,000.0