Note 9 - Property, Plant and Equipment - Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Total Property, Plant and Equipment	$ 5,351,120	$ 5,250,805
Less: Accumulated Depreciation, Depletion and Amortization	3,397,821	3,272,255
Total Property, Plant and Equipment, Net	1,953,299	1,978,550
Coal and Other Plant and Equipment [Member]
Total Property, Plant and Equipment	3,287,698	3,209,232
Mining Properties and Mineral Rights [Member]
Total Property, Plant and Equipment	894,573	881,551
Airshafts [Member]
Total Property, Plant and Equipment	479,540	473,866
Mine Development [Member]
Total Property, Plant and Equipment	360,810	357,479
Coal Advance Mining Royalties [Member]
Total Property, Plant and Equipment	$ 328,499	$ 328,677