Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Oil and natural gas properties, accumulated depreciation, depletion and amortization	$ 7,175	$ 12,950
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	65,000,000	65,000,000
Common stock, shares issued	10,141,512	10,054,816
Common stock, shares, outstanding	10,117,472	10,042,468
Treasury stock, shares	24,040	12,348