Investment in Laramie Energy, LLC - Additional Information (Detail) - USD ($)			3 Months Ended	12 Months Ended
	Oct. 18, 2018	Feb. 28, 2018	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Mar. 04, 2019	Mar. 01, 2016
Schedule of Equity Method Investments [Line Items]
Depreciation, depletion, and amortization				$ 86,121,000	$ 52,642,000	$ 45,989,000
Unrealized gain (loss) on derivative contracts				$ (9,350,000)	(2,122,000)	989,000
Laramie Energy Company
Schedule of Equity Method Investments [Line Items]
Ownership of Laramie Energy, LLC	46.00%	39.10%	46.00%	46.00%					42.30%
Impairment loss				$ 355,200,000
Equity method investments, fair value							$ 51,800,000
Equity method investment, aggregate cost							133,300,000
Impairment charge				81,515,000	0	0
Depreciation, depletion, and amortization				82,600,000	66,600,000	50,300,000
Unrealized gain (loss) on derivative contracts				4,300,000	(4,100,000)	$ 46,200,000
Amount of equity in underlying assets exceeding carrying value			$ 0	0			$ 161,800,000
Laramie Energy Company
Schedule of Equity Method Investments [Line Items]
Impairment loss			355,200,000
Disposal group, property, plant and equipment								$ 17,500,000
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	400,000,000
Current borrowing capacity			220,000,000	220,000,000
Balance outstanding on the revolving credit facility			$ 201,200,000	$ 201,200,000	$ 210,800,000
Capital Unit, Class A | Laramie Energy Company
Schedule of Equity Method Investments [Line Items]
Stock repurchased during period (in shares)	138,795
Stock repurchased during period	$ 14,800,000