Oil and Gas Properties - Net Capitalized Costs Related to Oil and Gas Producing Activities (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Extractive Industries [Abstract]
Unproved oil and gas properties	$ 64,653	$ 90,446
Proved oil and gas properties	222,713	221,299
Total costs	287,366	311,745
Less: accumulated depreciation, depletion and amortization	(62,901)	(48,252)
Net capitalized costs	$ 224,465	$ 263,493