Note 6 - Income Taxes - Schedule of Significant Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred Tax Asset:
Postretirement benefits other than pensions	$ 84,130	$ 101,673
Pneumoconiosis benefits	47,681	60,284
Asset retirement obligations	47,180	56,779
Workers' compensation	11,419	17,493
Compensation	5,203	5,158
State bonus, net of Federal	4,219	6,918
Long-term disability	1,931	2,757
Net operating loss	937	6,134
Operating lease liability	135	11,377
Mine subsidence	0	17,271
Salary retirement, deferred tax assets	0	9,446
Financing, deferred tax assets	0	2,077
Other	5,772	4,175
Total Deferred Tax Asset	208,607	301,542
Valuation Allowance	(937)	(2,879)
Net Deferred Tax Asset	207,670	298,663
Deferred Tax Liability:
Equity Partnerships	(99,811)	(35,570)
Property, plant and equipment	(40,064)	(172,026)
Advance mining royalties	(7,270)	(10,908)
Salary retirement, deferred tax liabilities	(2,739)	0
Financing, deferred tax liabilities	(640)	0
Right of use assets	(135)	(11,338)
Total Deferred Tax Liability	(150,659)	(229,842)
Net Deferred Tax Asset	$ 57,011	$ 68,821