REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	$ 313,355	$ 316,113	$ 1,102,272	$ 994,053
Coal Revenue
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	294,797	279,245	1,016,503	899,400
Terminal Revenue
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	16,115	15,065	47,995	42,806
Freight Revenue
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	$ 2,443	$ 21,803	$ 37,774	$ 51,847