Investment in Laramie Energy Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Payments to Acquire Equity Method Investments	$ 0	$ 55,000,000
Depreciation, depletion, and amortization	11,260,000	5,095,000
Unrealized loss (gain) on derivative contracts	$ (1,488,000)	1,609,000
Laramie Energy Company
Schedule of Equity Method Investments [Line Items]
Ownership of Laramie Energy, LLC	42.30%
Payments to Acquire Equity Method Investments			$ 55,000,000	$ 27,500,000
Line credit maximum borrowing amount	$ 400,000,000
Asset borrowing base currently at	210,000,000
Balance outstanding on the revolving credit facility	121,000,000
Depreciation, depletion, and amortization	13,300,000	7,600,000
Unrealized loss (gain) on derivative contracts	(24,200,000)	$ (5,900,000)
Amount of equity in underlying assets exceeding carrying value	$ 66,500,000		$ 67,800,000
Amortization of natural gas and oil properties	15 years