Basis of Presentation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Oil and Condensate Revenue	$ 2,946	$ 2,302
Basic (in dollars per share)	$ 0.68	$ 1.87
Diluted (in dollars per share)	$ 0.68	$ 1.86
Gas Gathering, Transportation, Marketing and Processing Costs	$ 3,359	$ 2,551
Other Pension, Postretirement and Supplemental Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	$ 100	$ 100