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, 2018	Dec. 31, 2017
Oil and gas properties, successful efforts method:
Accumulated impairment	$ (121,100)	$ (148,200)
Proved properties, net of accumulated impairments	755,443	605,039
Unproved properties, net of accumulated impairments	266,140	275,025
Land	5,382	5,534
Total oil and gas properties, net of accumulated impairments	1,026,965	885,598
Accumulated depreciation, depletion and amortization	(127,256)	(118,028)
Net oil and gas properties	899,709	767,570
Proved property
Oil and gas properties, successful efforts method:
Proved properties	830,843	708,646
Accumulated impairment	(75,400)	(103,608)
Proved properties, net of accumulated impairments	755,443	605,038
Unproved property
Oil and gas properties, successful efforts method:
Accumulated impairment	(45,688)	(44,543)
Unproved properties	311,828	319,569
Unproved properties, net of accumulated impairments	$ 266,140	$ 275,026