Investment in Laramie Energy, LLC - Additional Information (Details) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 0			$ 0		$ 46,905,000
Depreciation, depletion, and amortization	$ 22,128,000		$ 21,919,000	43,411,000	$ 42,876,000
Unrealized gain (loss) on derivative contracts				$ (2,048,000)	(21,086,000)
Laramie Energy Company
Schedule of Equity Method Investments [Line Items]
Ownership interest in Laramie Energy, LLC	46.00%			46.00%
Equity method investments, fair value	$ 0	$ 1,900,000		$ 0		$ 46,905,000
Equity method investment, aggregate cost		47,200,000
Impairment of our investment in Laramie Energy		$ 45,300,000		45,294,000
Equity method investments	0			0
Depreciation, depletion, and amortization	10,000,000.0		21,000,000.0	19,300,000	42,400,000
Unrealized gain (loss) on derivative contracts	(4,100,000)		$ 8,400,000	(1,700,000)	$ 11,100,000
Revolving Credit Facility | Laramie Energy Company
Schedule of Equity Method Investments [Line Items]
Credit facility, maximum borrowing amount	400,000,000			400,000,000
Asset borrowing base	202,500,000			202,500,000
Balance outstanding on the revolving credit facility	$ 197,500,000			$ 197,500,000