Significant Accounting Policies - Depreciation (Details)	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Depreciation and amortization expense included in operations
Depreciation and amortization expense included in operations	$ 151,000	$ 176,000	$ 188,000
Depletion of mineral rights	$ 514,000	$ 510,000	$ 650,000
Office and field equipment useful lives minimum(Years)	5
Office and field equipment useful lives maximum(Years)	30