REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	$ 371,182	$ 404,800	$ 728,165	$ 788,917
Coal Revenue
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	350,620	370,697	683,123	721,706
Terminal Revenue
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	16,708	16,659	34,526	31,880
Freight Revenue
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	$ 3,854	$ 17,444	$ 10,516	$ 35,331