Note 7 - Revenue - Domestic Revenues an Export Revenues (Details) $ in Thousands	3 Months Ended
Mar. 31, 2020 USD ($) T	Mar. 31, 2019 USD ($)
REVENUES
Revenues	$ 41,935	$ 57,460
Term of domestic sales contracts	1 year
Outstanding performance obligation, mass \| T	1.1
Domestic Coal Revenues
REVENUES
Revenues	$ 30,532	36,571
Export Coal Revenues
REVENUES
Revenues	$ 11,403	$ 20,889

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration