Summary of Property and Equipment (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) $ / bbl	Mar. 31, 2017 USD ($) $ / bbl	Dec. 31, 2017 USD ($)
Property, Plant and Equipment [Abstract]
Proved Oil and Gas Property, Full Cost Method	$ 624,747		$ 460,029
Unproved Oil and Gas Property, Full Cost Method	137,722		117,634
Oil and Gas Property, Full Cost Method, Gross	762,469		577,663
Other property and equipment	13,702		12,712
Total properties and equipment	776,171		590,375
Accumulated depreciation, depletion and amortization	(84,888)		(61,316)
Property and equipment, net (successful efforts method)	691,283		529,059
Unproved Oil and Gas Property excluded	137,700		$ 117,600
Undeveloped Leasehold Costs Transferred	100
Capitalized Costs, Proved Properties	700	$ 600
Interest Costs Capitalized	$ 2,200	$ 100
Amortization Expense Per Physical Unit of Production | $ / bbl	15.2	11.47