Summary of Property and Equipment (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) $ / bbl	Sep. 30, 2017 USD ($) $ / bbl	Dec. 31, 2017 USD ($)
Property, Plant and Equipment [Abstract]
Proved Oil and Gas Property, Full Cost Method	$ 864,426		$ 460,029
Unproved Oil and Gas Property, Full Cost Method	132,576		117,634
Oil and Gas Property, Full Cost Method, Gross	997,002		577,663
Other property and equipment	18,701		12,712
Total properties and equipment	1,015,703		590,375
Accumulated depreciation, depletion and amortization	(156,937)		(61,316)
Property and equipment, net (successful efforts method)	858,766		529,059
Unproved Oil and Gas Property excluded	132,600		$ 117,600
Capitalized Exploratory Well Costs	18,700
Undeveloped Leasehold Costs Transferred	11,400
Capitalized Costs, Proved Properties	2,400	$ 1,600
Interest Costs Capitalized	$ 7,100	$ 100
Amortization Expense Per Physical Unit of Production | $ / bbl	15.83	11.93