Note 3 - Revenue - Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Total Revenue from Contracts with Customers	$ 303,222	$ 121,296	$ 633,982	$ 396,396
Domestic Coal Revenue [Member]
Total Revenue from Contracts with Customers	117,161	69,317	276,377	217,427
Export Coal Revenue [Member]
Total Revenue from Contracts with Customers	142,671	32,996	268,990	140,338
Terminal Revenue [Member]
Total Revenue from Contracts with Customers	17,380	15,898	35,592	32,399
Freight Revenue [Member]
Total Revenue from Contracts with Customers	$ 26,010	$ 3,085	$ 53,023	$ 6,232