Supplemental Oil and Gas Disclosures (Unaudited) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Results of Operations for Producing Activities Detail [Table]
Oil and gas sales revenues	$ 538	$ 751	$ 2,438
Production (lifting) costs	1,234	643	921
Excess decommissioning and abandonment costs	0	2,593	2,665
Accretion expense	1,382	1,362	1,375
Results of Operations, Income before Income Taxes	(2,078)	(3,847)	(2,523)
Income tax expense (benefit)	0	0	0
Results of oil and gas producing activities	$ (2,078)	$ (3,847)	$ (2,523)