Unproved Oil and Gas Properties, Full Cost Method (Details) - USD ($) $ in Thousands		6 Months Ended		12 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Excluded from amortization base:
Drilling costs, and other operational related costs		$ 1,243		$ 1,242
Capitalized salary costs		1,668		1,579
Capitalized interest costs		715		677
Legal costs, license fees and other preparation costs		3,484		3,216
Other costs		11
Total unproved oil and gas properties, full cost method	[1]	7,121		$ 6,714
Oil and Gas Properties [Member]
Excluded from amortization base:
Drilling costs, and other operational related costs		159
Other costs		69
Total unproved oil and gas properties, full cost method		$ 228

[1] The unproved oil and gas properties balance at June 30, 2019 and at December 31, 2018 contains approximately $136,000 and $2,946,000, respectively, in unpaid amounts.