GUARANTOR SUBSIDIARIES FINANCIAL INFORMATION - Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Current Assets:
Cash and Cash Equivalents	$ 191,719	$ 153,979	$ 6,638	$ 13,311
Trade	127,348	131,545
Other Receivables	32,359	36,552
Inventories	60,766	53,420
Prepaid Expenses	24,855	23,744
Total Current Assets	437,047	399,240
Property, Plant and Equipment:
Property, Plant and Equipment	4,722,123	4,676,353
Less—Accumulated Depreciation, Depletion and Amortization	2,599,775	2,554,056
Total Property, Plant and Equipment—Net	2,122,348	2,122,297
Other Assets:
Deferred Income Taxes	67,538	75,065
Affiliated Credit Facility	0	0
Investment in Affiliates	0	0
Other	102,183	110,497
Total Other Assets	169,721	185,562
TOTAL ASSETS	2,729,116	2,707,099	$ 2,685,076
Current Liabilities:
Accounts Payable	84,691	109,100
Accounts Payable (Recoverable)-Related Parties	0	0
Current Portion of Long-Term Debt	18,386	22,482
Other Accrued Liabilities	285,132	290,627
Total Current Liabilities	388,209	422,209
Long-Term Debt	866,337	865,289
Deferred Credits and Other Liabilities:
Postretirement Benefits Other Than Pensions	549,244	554,099
Pneumoconiosis Benefits	150,541	149,868
Asset Retirement Obligations	231,783	228,343
Workers’ Compensation	66,280	66,648
Salary Retirement	48,361	52,960
Other	19,173	24,042
Total Deferred Credits and Other Liabilities	1,065,382	1,075,960
Total CONSOL Energy Inc. Stockholders' Equity	267,386	204,260
Noncontrolling Interest	141,802	139,381
TOTAL LIABILITIES AND EQUITY	2,729,116	2,707,099
Elimination
Current Assets:
Cash and Cash Equivalents	0	0
Trade	0	0
Other Receivables	0	0
Inventories	0	0
Prepaid Expenses	0	0
Total Current Assets	0	0
Property, Plant and Equipment:
Property, Plant and Equipment	0	0
Less—Accumulated Depreciation, Depletion and Amortization	0	0
Total Property, Plant and Equipment—Net	0	0
Other Assets:
Deferred Income Taxes	0	0
Affiliated Credit Facility	(156,228)	(165,110)
Investment in Affiliates	(682,407)	(645,157)
Other	0	0
Total Other Assets	(838,635)	(810,267)
TOTAL ASSETS	(838,635)	(810,267)
Current Liabilities:
Accounts Payable	2,220	18
Accounts Payable (Recoverable)-Related Parties	(156,228)	(163,069)
Current Portion of Long-Term Debt	0	0
Other Accrued Liabilities	(2,179)	(4,874)
Total Current Liabilities	(156,187)	(167,925)
Long-Term Debt	(156,228)	(165,110)
Deferred Credits and Other Liabilities:
Postretirement Benefits Other Than Pensions	0	0
Pneumoconiosis Benefits	0	0
Asset Retirement Obligations	0	0
Workers’ Compensation	0	0
Salary Retirement	0	0
Other	0	0
Total Deferred Credits and Other Liabilities	0	0
Total CONSOL Energy Inc. Stockholders' Equity	(668,022)	(616,613)
Noncontrolling Interest	141,802	139,381
TOTAL LIABILITIES AND EQUITY	(838,635)	(810,267)
CCR Non-Guarantor
Current Liabilities:
Accounts Payable (Recoverable)-Related Parties	935	3,071
Parent Issuer | Reportable Legal Entities
Current Assets:
Cash and Cash Equivalents	190,564	152,235
Trade	0	0
Other Receivables	14,645	17,702
Inventories	0	0
Prepaid Expenses	7,034	5,745
Total Current Assets	212,243	175,682
Property, Plant and Equipment:
Property, Plant and Equipment	0	0
Less—Accumulated Depreciation, Depletion and Amortization	0	0
Total Property, Plant and Equipment—Net	0	0
Other Assets:
Deferred Income Taxes	67,538	75,065
Affiliated Credit Facility	156,228	165,110
Investment in Affiliates	682,407	645,157
Other	40,642	44,177
Total Other Assets	946,815	929,509
TOTAL ASSETS	1,159,058	1,105,191
Current Liabilities:
Accounts Payable	10,521	20,014
Accounts Payable (Recoverable)-Related Parties	(2,291)	(2,291)
Current Portion of Long-Term Debt	0	0
Other Accrued Liabilities	106,974	101,994
Total Current Liabilities	115,204	119,717
Long-Term Debt	728,107	728,254
Deferred Credits and Other Liabilities:
Postretirement Benefits Other Than Pensions	0	0
Pneumoconiosis Benefits	0	0
Asset Retirement Obligations	0	0
Workers’ Compensation	0	0
Salary Retirement	48,361	52,960
Other	0	0
Total Deferred Credits and Other Liabilities	48,361	52,960
Total CONSOL Energy Inc. Stockholders' Equity	267,386	204,260
Noncontrolling Interest	0	0
TOTAL LIABILITIES AND EQUITY	1,159,058	1,105,191
Guarantor | Reportable Legal Entities
Current Assets:
Cash and Cash Equivalents	369	105
Trade	0	0
Other Receivables	16,283	16,880
Inventories	46,645	41,117
Prepaid Expenses	13,417	13,568
Total Current Assets	76,714	71,670
Property, Plant and Equipment:
Property, Plant and Equipment	3,802,245	3,765,885
Less—Accumulated Depreciation, Depletion and Amortization	2,106,017	2,070,646
Total Property, Plant and Equipment—Net	1,696,228	1,695,239
Other Assets:
Deferred Income Taxes	0	0
Affiliated Credit Facility	0	0
Investment in Affiliates	0	0
Other	46,858	50,846
Total Other Assets	46,858	50,846
TOTAL ASSETS	1,819,800	1,817,755
Current Liabilities:
Accounts Payable	54,070	66,271
Accounts Payable (Recoverable)-Related Parties	36,221	36,221
Current Portion of Long-Term Debt	16,568	22,405
Other Accrued Liabilities	136,810	149,425
Total Current Liabilities	243,669	274,322
Long-Term Debt	134,462	135,390
Deferred Credits and Other Liabilities:
Postretirement Benefits Other Than Pensions	549,244	554,099
Pneumoconiosis Benefits	146,336	146,035
Asset Retirement Obligations	221,975	218,728
Workers’ Compensation	62,827	63,244
Salary Retirement	0	0
Other	18,570	23,435
Total Deferred Credits and Other Liabilities	998,952	1,005,541
Total CONSOL Energy Inc. Stockholders' Equity	442,717	402,502
Noncontrolling Interest	0	0
TOTAL LIABILITIES AND EQUITY	1,819,800	1,817,755
Non-Guarantor | Reportable Legal Entities
Current Assets:
Cash and Cash Equivalents	38	106
Trade	127,348	131,545
Other Receivables	0	0
Inventories	0	0
Prepaid Expenses	0	3
Total Current Assets	127,386	131,654
Property, Plant and Equipment:
Property, Plant and Equipment	0	0
Less—Accumulated Depreciation, Depletion and Amortization	0	0
Total Property, Plant and Equipment—Net	0	0
Other Assets:
Deferred Income Taxes	0	0
Affiliated Credit Facility	0	0
Investment in Affiliates	0	0
Other	0	0
Total Other Assets	0	0
TOTAL ASSETS	127,386	131,654
Current Liabilities:
Accounts Payable	8	8
Accounts Payable (Recoverable)-Related Parties	122,298	129,139
Current Portion of Long-Term Debt	0	0
Other Accrued Liabilities	0	(20)
Total Current Liabilities	122,306	129,127
Long-Term Debt	0	1,572
Deferred Credits and Other Liabilities:
Postretirement Benefits Other Than Pensions	0	0
Pneumoconiosis Benefits	0	0
Asset Retirement Obligations	0	0
Workers’ Compensation	0	0
Salary Retirement	0	0
Other	0	0
Total Deferred Credits and Other Liabilities	0	0
Total CONSOL Energy Inc. Stockholders' Equity	5,080	955
Noncontrolling Interest	0	0
TOTAL LIABILITIES AND EQUITY	127,386	131,654
Non-Guarantor | CCR Non-Guarantor | Reportable Legal Entities
Current Assets:
Cash and Cash Equivalents	748	1,533
Trade	0	0
Other Receivables	1,431	1,970
Inventories	14,121	12,303
Prepaid Expenses	4,404	4,428
Total Current Assets	20,704	20,234
Property, Plant and Equipment:
Property, Plant and Equipment	919,878	910,468
Less—Accumulated Depreciation, Depletion and Amortization	493,758	483,410
Total Property, Plant and Equipment—Net	426,120	427,058
Other Assets:
Deferred Income Taxes	0	0
Affiliated Credit Facility	0	0
Investment in Affiliates	0	0
Other	14,683	15,474
Total Other Assets	14,683	15,474
TOTAL ASSETS	461,507	462,766
Current Liabilities:
Accounts Payable	17,872	22,789
Accounts Payable (Recoverable)-Related Parties	0	0
Current Portion of Long-Term Debt	1,818	77
Other Accrued Liabilities	43,527	44,102
Total Current Liabilities	63,217	66,968
Long-Term Debt	159,996	165,183
Deferred Credits and Other Liabilities:
Postretirement Benefits Other Than Pensions	0	0
Pneumoconiosis Benefits	4,205	3,833
Asset Retirement Obligations	9,808	9,615
Workers’ Compensation	3,453	3,404
Salary Retirement	0	0
Other	603	607
Total Deferred Credits and Other Liabilities	18,069	17,459
Total CONSOL Energy Inc. Stockholders' Equity	220,225	213,156
Noncontrolling Interest	0	0
TOTAL LIABILITIES AND EQUITY	$ 461,507	$ 462,766