Related Party Transactions (Schedule of Related Party Disclosures) (Details) - Majority Shareholder - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Total Services from CONSOL Energy	$ 6,612	$ 8,077	$ 15,719
Operating and Other Costs
Related Party Transaction [Line Items]
Total Services from CONSOL Energy	3,503	4,251	6,793
Selling, General and Administrative Costs
Related Party Transaction [Line Items]
Total Services from CONSOL Energy	$ 3,109	$ 3,826	$ 8,926