RELATED PARTY TRANSACTIONS - Narrative (Details)	1 Months Ended			3 Months Ended	9 Months Ended		12 Months Ended
	Oct. 31, 2017 shares	Sep. 30, 2016 USD ($) $ / shares shares	Jul. 31, 2015 USD ($) $ / shares shares	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($) business $ / shares shares	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Jul. 31, 2018 USD ($)	Nov. 30, 2017	Nov. 28, 2017 USD ($)
Related Party Transaction [Line Items]
Separation and distribution costs							$ 40,545,000
Payment of separation and distribution costs					$ 18,234,000
Number of independent businesses | business					2
Origination fees					$ 2,851,000	$ 0
Net proceeds from initial public offering			$ 342,711,000
Undivided interest (as a percent)									75.00%
Net payable				$ 0	$ 0		0
Shares repurchased (in shares) | shares					281,272
Average share price (in dollars per share) | $ / shares					$ 40.03
CONSOL Thermal Holdings LLC
Related Party Transaction [Line Items]
Undivided interest (as a percent)		5.00%
Cash consideration		$ 21,500,000
Equity consideration		$ 67,300,000
Weighted average trading price (in dollars per share) | $ / shares		$ 14.79
Price premium (as a percent)		15.00%
CONSOL Coal Resources LP
Related Party Transaction [Line Items]
Net payable				1,573,000	$ 1,573,000		3,071,000
Preferred Class A | CONSOL Thermal Holdings LLC
Related Party Transaction [Line Items]
Preferred units issued (in shares) | shares	3,956,496	3,956,496
Issue price (in dollars per share) | $ / shares		$ 17.01
Consol Coal Resources LP Units
Related Party Transaction [Line Items]
Stock and debt repurchase additional amount authorized								$ 25,000,000
Shares repurchased (in shares) | shares					77,536
Average share price (in dollars per share) | $ / shares					$ 17.86
Senior Secured Revolving Credit Facility | Line of Credit
Related Party Transaction [Line Items]
Maximum borrowing capacity			400,000,000
Initial draw on line of credit			200,000,000
Origination fees			3,000,000
Net proceeds line of credit			$ 197,000,000
CNX Resources Corporation
Related Party Transaction [Line Items]
Accounts payable, related parties				473,000	$ 473,000		12,540,000
Notes receivable, related parties				11,570,000	11,570,000		15,415,000
Other receivables - related parties				5,282,000	5,282,000		4,500,000
Accounts receivable, related parties, noncurrent				6,288,000	6,288,000		$ 10,915,000
CNX Coal Resources LP
Related Party Transaction [Line Items]
Units sold in initial public offering (in shares) | shares			5,000,000
Initial public offering share price (in dollars per share) | $ / shares			$ 15.00
Net proceeds initial public offering			$ 75,000,000
Over-allotment option (in shares) | shares			561,067
Affiliated Entity | Affiliated Company Credit Agreement | CONSOL Coal Resources LP
Related Party Transaction [Line Items]
Maximum borrowing capacity										$ 275,000,000
Line of credit amount drawn										$ 201,000,000
Interest expense				$ 1,832,000	$ 5,942,000
Minimum | Affiliated Entity | Affiliated Company Credit Agreement | CONSOL Coal Resources LP
Related Party Transaction [Line Items]
Stated interest rate (as a percent)				3.75%	3.75%
Maximum | Affiliated Entity | Affiliated Company Credit Agreement | CONSOL Coal Resources LP
Related Party Transaction [Line Items]
Stated interest rate (as a percent)				4.75%	4.75%