Unproved Oil and Gas Properties, Full Cost Method (Details 1) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Excluded from amortization base:
Drilling costs, and other operational related costs		$ 13,614	$ 13,229	$ 458
Capitalized salary costs		551	455	402
Capitalized interest costs		331	346
Legal costs, license fees and other preparation costs		1,168	1,069	512
Other costs		261
Impairment of unproved oil and gas properties		30,906
Changes in Unproved oil and gas properties	[1]	$ (14,981)	$ 15,298	$ 1,375

[1] Inclusive of non-cash amounts of approximately $3,625,000, $4,478,000 and $238,000 during the years 2018, 2017 and 2016, respectively