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Operating Segments (Narrative) (Details)
6 Months Ended
Jun. 30, 2018
Dorad Energy Ltd [Member]  
Statement Line Items [Line Items]  
Proportion of ownership interest 9.375%
Groen Gas Goor B.V [Member]  
Statement Line Items [Line Items]  
Proportion of ownership interest 51.00%
Chashgal Elyon Ltd. [Member]  
Statement Line Items [Line Items]  
Proportion of ownership interest 75.00%