Supplemental Information On Oil And Gas Exploration And Production Activities (Unaudited) - Summary of Capitalized Costs, Impairment, and Depreciation, Depletion and Amortization (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Oil and gas properties, successful efforts method:
Accumulated impairment	$ (162,700)	$ (155,900)
Proved properties, net of accumulated impairments	363,072	283,644
Unproved properties, net of accumulated impairments	51,723	34,609
Total oil and gas properties, net of accumulated impairments	414,795	318,253
Accumulated depreciation, depletion and amortization	(145,393)	(119,920)
Net oil and gas properties	269,402	198,333
Proved Property [Member]
Oil and gas properties, successful efforts method:
Proved properties	476,832	394,532
Accumulated impairment	(113,760)	(110,888)
Proved properties, net of accumulated impairments	363,072	283,644
Unproved Property [Member]
Oil and gas properties, successful efforts method:
Unproved properties	100,612	79,619
Accumulated impairment	(48,889)	(45,010)
Unproved properties, net of accumulated impairments	$ 51,723	$ 34,609