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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net Income	$ 46,034	$ 9,084	$ 52,709	$ 70,958	$ (24,640)	$ 8,518	$ 52,246	$ 46,445	$ 178,785	$ 82,569	$ 50,450
Less: Net Income Attributable to Noncontrolling Interest	6,362	3,350	7,547	8,550	4,373	790	4,313	5,464	25,809	14,940	8,954
Net Income Attributable to CONSOL Energy Inc. Shareholders	$ 39,672	$ 5,734	$ 45,162	$ 62,408	$ (29,013)	$ 7,728	$ 47,933	$ 40,981	$ 152,976	$ 67,629	$ 41,496
Denominator:
Weighted-average shares of common stock outstanding (in shares)									27,928,245	27,968,188	27,967,509
Effect of dilutive shares (in shares)									491,517	206,046	0
Weighted-average diluted shares of common stock outstanding (in shares)									28,419,762	28,174,234	27,967,509
Earnings per Share:
Basic (in dollars per share)									$ 5.48	$ 2.42	$ 1.48
Dilutive (in dollars per share)									$ 5.38	$ 2.40	$ 1.48