Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers									$ 1,375,559	$ 1,472,790	$ 1,321,412
Coal Revenue
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	$ 303,865	$ 301,542	$ 350,620	$ 332,502	$ 347,789	$ 294,797	$ 370,697	$ 351,009	1,288,529	1,364,292	1,187,654
Terminal Revenue
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	16,534	16,303	16,708	17,818	16,931	16,115	16,659	15,221	67,363	64,926	60,066
Freight Revenue
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	$ 5,552	$ 3,599	$ 3,854	$ 6,662	$ 5,798	$ 2,443	$ 17,444	$ 17,887	$ 19,667	$ 43,572	$ 73,692