REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	$ 321,444	$ 313,355	$ 1,049,609	$ 1,102,272
Coal Revenue
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	301,542	294,797	984,665	1,016,503
Terminal Revenue
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	16,303	16,115	50,829	47,995
Freight Revenue
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	$ 3,599	$ 2,443	$ 14,115	$ 37,774

Amount, excluding 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 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

Reference 2: 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

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