Note 4 - Miscellaneous Other Income - Miscellaneous Other Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Contract Buyout	$ 44,703	$ 9,959	$ 350
Sale of Certain Mining Rights	39,437	0	0
Sale of Certain Coal Lease Contracts	17,847	0	0
Royalty Income - Non-Operated Coal	12,032	22,208	24,722
Litigation Proceeds	8,624	0	0
Rental Income	1,314	2,517	3,804
Interest Income	1,230	2,937	2,146
Property Easements and Option Income	907	1,631	5,644
Purchased Coal Sales	0	12,385	19,152
Other	792	1,712	2,842
Miscellaneous Other Income	$ 126,886	$ 53,349	$ 58,660