Note 23 - Segment Information - Industry Segment (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Total Revenue from Contracts with Customers		$ 879,462	$ 1,375,559	$ 1,472,790
Adjusted EBITDA		261,523	405,936	484,736
Assets, Total		2,523,366	2,693,802	2,760,727
Depreciation, Depletion and Amortization		210,760	207,097	201,264
Capital Expenditures		86,004	169,739	145,749
Coal Revenue [Member]
Total Revenue from Contracts with Customers	[1]	772,662	1,288,529	1,364,292
Terminal Revenue [Member]
Total Revenue from Contracts with Customers		66,810	67,363	64,926
Freight Revenue [Member]
Total Revenue from Contracts with Customers		39,990	19,667	43,572
Intersegment Eliminations [Member]
Total Revenue from Contracts with Customers		0	0	0
Adjusted EBITDA		0	0	0
Assets, Total		0	0	0
Depreciation, Depletion and Amortization		0	0	0
Capital Expenditures		0	0	0
Intersegment Eliminations [Member] | Coal Revenue [Member]
Total Revenue from Contracts with Customers	[1]	0	0	0
Intersegment Eliminations [Member] | Terminal Revenue [Member]
Total Revenue from Contracts with Customers		0	0	0
Intersegment Eliminations [Member] | Freight Revenue [Member]
Total Revenue from Contracts with Customers		0	0	0
Pennsylvania Mining Complex [Member] | Operating Segments [Member]
Total Revenue from Contracts with Customers		811,353	1,308,196	1,407,864
Adjusted EBITDA		228,211	394,354	479,969
Assets, Total		1,864,514	1,981,721	1,894,209
Depreciation, Depletion and Amortization		198,272	185,616	178,969
Capital Expenditures		70,195	148,709	124,570
Pennsylvania Mining Complex [Member] | Operating Segments [Member] | Coal Revenue [Member]
Total Revenue from Contracts with Customers	[1]	771,363	1,288,529	1,364,292
Pennsylvania Mining Complex [Member] | Operating Segments [Member] | Terminal Revenue [Member]
Total Revenue from Contracts with Customers		0	0	0
Pennsylvania Mining Complex [Member] | Operating Segments [Member] | Freight Revenue [Member]
Total Revenue from Contracts with Customers		39,990	19,667	43,572
CONSOL Marine Terminal [Member] | Operating Segments [Member]
Total Revenue from Contracts with Customers		66,810	67,363	64,926
Adjusted EBITDA		44,356	44,491	40,901
Assets, Total		108,711	87,558	84,929
Depreciation, Depletion and Amortization		5,095	4,078	3,782
Capital Expenditures		1,455	6,675	5,475
CONSOL Marine Terminal [Member] | Operating Segments [Member] | Coal Revenue [Member]
Total Revenue from Contracts with Customers	[1]	0	0	0
CONSOL Marine Terminal [Member] | Operating Segments [Member] | Terminal Revenue [Member]
Total Revenue from Contracts with Customers		66,810	67,363	64,926
CONSOL Marine Terminal [Member] | Operating Segments [Member] | Freight Revenue [Member]
Total Revenue from Contracts with Customers		0	0	0
Other Segments [Member] | Operating Segments [Member]
Total Revenue from Contracts with Customers		1,299	0	0
Adjusted EBITDA		(11,044)	(32,909)	(36,134)
Assets, Total		550,141	624,523	781,589
Depreciation, Depletion and Amortization		7,393	17,403	18,513
Capital Expenditures		14,354	14,355	15,704
Other Segments [Member] | Operating Segments [Member] | Coal Revenue [Member]
Total Revenue from Contracts with Customers	[1]	1,299	0	0
Other Segments [Member] | Operating Segments [Member] | Terminal Revenue [Member]
Total Revenue from Contracts with Customers		0	0	0
Other Segments [Member] | Operating Segments [Member] | Freight Revenue [Member]
Total Revenue from Contracts with Customers		$ 0	$ 0	$ 0

[1] For the years ended December 31, 2020, 2019 and 2018 , the PAMC segment had revenues from the following customers, each comprising over 10% of the Company's total sales: For the Years Ended December 31, 2020 2019 2018 Customer A $ 134,354 $ 242,703 $ 283,703 Customer B $ 173,461 $ 446,403 $ 274,755 Customer C $ 116,536 $ 215,099 $ 214,152