Note 3 - Revenue - Revenue (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Total Revenue from Contracts with Customers		$ 879,462	$ 1,375,559	$ 1,472,790
Coal Revenue [Member]
Total Revenue from Contracts with Customers	[1]	772,662	1,288,529	1,364,292
Terminal Revenue [Member]
Total Revenue from Contracts with Customers		66,810	67,363	64,926
Freight Revenue [Member]
Total Revenue from Contracts with Customers		$ 39,990	$ 19,667	$ 43,572

[1] For the years ended December 31, 2020, 2019 and 2018 , the PAMC segment had revenues from the following customers, each comprising over 10% of the Company's total sales: For the Years Ended December 31, 2020 2019 2018 Customer A $ 134,354 $ 242,703 $ 283,703 Customer B $ 173,461 $ 446,403 $ 274,755 Customer C $ 116,536 $ 215,099 $ 214,152