Significant Accounting Policies (Schedule of Basic and Dilutive Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net Income	$ (24,640)	$ 8,518	$ 52,246	$ 46,445	$ 22,914	$ 4,751	$ 13,901	$ 8,884	$ 82,569	$ 50,450	$ 317,421
Less: Net Income Attributable to Noncontrolling Interest	4,373	790	4,313	5,464	4,413	2,248	1,179	1,114	14,940	8,954	10,410
Net Income Attributable to CONSOL Energy Shareholders	$ (29,013)	$ 7,728	$ 47,933	$ 40,981	$ 18,501	$ 2,503	$ 12,722	$ 7,770	$ 67,629	$ 41,496	$ 307,011
Denominator:
Weighted-average shares of common stock outstanding (in shares)									27,968	27,968	27,968
Effect of dilutive shares (in shares)									206	0	0
Weighted-average diluted shares of common stock outstanding (in shares)									28,174	27,968	27,968
Earnings Per Share:
Basic (in dollars per share)									$ 2.42	$ 1.48	$ 10.98
Dilutive (in dollars per share)									$ 2.40	$ 1.48	$ 10.98