Unevaluated Property (Details Textuals)	12 Months Ended
	Dec. 31, 2018
Minimum
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Anticipated Timing of Inclusion of Costs in Amortization Calculation	5 years
Maximum
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Anticipated Timing of Inclusion of Costs in Amortization Calculation	10 years