Summary of Property and Equipment (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) $ / bbl	Jun. 30, 2017 USD ($) $ / bbl	Dec. 31, 2017 USD ($)
Property, Plant and Equipment [Abstract]
Proved Oil and Gas Property, Full Cost Method	$ 756,863		$ 460,029
Unproved Oil and Gas Property, Full Cost Method	134,943		117,634
Oil and Gas Property, Full Cost Method, Gross	891,806		577,663
Other property and equipment	16,105		12,712
Total properties and equipment	907,911		590,375
Accumulated depreciation, depletion and amortization	(116,287)		(61,316)
Property and equipment, net (successful efforts method)	791,624		529,059
Unproved Oil and Gas Property excluded	134,900		$ 117,600
Undeveloped Leasehold Costs Transferred	5,600
Capitalized Costs, Proved Properties	1,600	$ 1,100
Interest Costs Capitalized	$ 4,700	$ 100
Amortization Expense Per Physical Unit of Production | $ / bbl	15.36	11.74