Investment in Laramie Energy, LLC - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Depreciation, depletion, and amortization	$ 20,957,000	$ 13,037,000
Unrealized gain (loss) on derivative contracts	$ (5,255,000)	846,000
Laramie Energy Company
Schedule of Equity Method Investments [Line Items]
Ownership interest in Laramie Energy, LLC	46.00%
Depreciation, depletion, and amortization	$ 21,400,000	14,900,000
Unrealized gain (loss) on derivative contracts	2,700,000	$ 4,600,000
Amount of equity in underlying assets exceeding carrying value by	$ 83,600,000		$ 85,200,000
Amortization of natural gas and oil properties	15 years
Revolving Credit Facility | Laramie Energy Company
Schedule of Equity Method Investments [Line Items]
Credit facility, maximum borrowing amount	$ 400,000,000
Asset borrowing base	240,000,000
Balance outstanding on the revolving credit facility	$ 192,800,000