Significant Accounting Policies - Depreciation (Details)	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Depreciation and amortization expense included in operations
Depreciation and amortization expense included in operations	$ 352,000	$ 151,000	$ 176,000
Depletion of mineral rights	$ 310,000	$ 514,000	$ 510,000
Property and equipment to operations over their estimated service lives minimum (Years)	5
Property and equipment to operations over their estimated service lives maximum (Years)	40
Office and field equipment useful lives range minimum (years)	5
Office and field equipment useful lives range maximum (years)	30