Variable Interest Entities Investment in Affiliates (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Equity Method [Roll Forward]
Balance at December 31, 2016		$ 175,371	$ 169,208	$ 169,208
Equity in Earnings		4,688	34,810	48,346
Distributions				(42,183)
Asset Transfer				0
Balance at December 31, 2017				175,371
CNX Gathering LLC [Member]
Equity Method [Roll Forward]
Balance at December 31, 2016		141,117	151,075	151,075
Equity in Earnings				9,823
Distributions				(17,254)
Asset Transfer				(2,527)
Balance at December 31, 2017				141,117
CNXM [Member]
Equity Method [Roll Forward]
Balance at December 31, 2016		$ 34,254	18,133	18,133
Equity in Earnings				38,523
Distributions				(24,929)
Asset Transfer				2,527
Balance at December 31, 2017				$ 34,254
Other Operating Income (Expense) [Member] | CNX Gathering LLC [Member]
Equity Method [Roll Forward]
Equity in Earnings	$ 2,350		4,500
Other Operating Income (Expense) [Member] | CNXM [Member]
Equity Method [Roll Forward]
Equity in Earnings	9,685		29,469
Transportation, Gathering and Compression [Member] | CNX Gathering LLC [Member]
Equity Method [Roll Forward]
Equity in Earnings	217		702
Transportation, Gathering and Compression [Member] | CNXM [Member]
Equity Method [Roll Forward]
Equity in Earnings	$ 32,639		$ 98,388