Note 3 - Revenue - Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Total Revenue from Contracts with Customers	$ 292,016	$ 214,292	$ 925,998	$ 610,688
Domestic Coal Revenue [Member]
Total Revenue from Contracts with Customers	152,311	144,171	428,688	361,598
Export Coal Revenue [Member]
Total Revenue from Contracts with Customers	106,249	40,204	375,239	180,542
Terminal Revenue [Member]
Total Revenue from Contracts with Customers	14,108	17,008	49,700	49,407
Freight Revenue [Member]
Total Revenue from Contracts with Customers	$ 19,348	$ 12,909	$ 72,371	$ 19,141