Note 11 - Employee Benefits (Details Textual)	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	100.00%
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	4.00%
Participants in Employee Health Plan	2,221
Health Care Cap Per Person	$ 200,000
Insured Capped Maximum Exposure, Health Care	19,000,000.0
Employee Benefit Costs	15,649,000	$ 19,465,000
Workers' compensation costs	1,900,000	3,100,000
Insured Maximum Exposure Per Employee	1,000,000
Aggregate Insurance Deductible for Employees	$ 4,000,000
Percentage Claims Are Below Average of Peers, Underground Coal Mining	24.00%
Operating Expense [Member]
Employee Benefit Costs	$ 15,000,000.0	$ 18,900,000