Note 6 - Income Taxes - Schedule of Reconciliation of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statutory U.S. federal income tax rate, amount	$ 7,436	$ (1,941)	$ 20,600
Statutory U.S. federal income tax rate, percent	21.00%	21.00%	21.00%
State income taxes, net of federal tax benefit, amount	$ (642)	$ (1,109)	$ 3,125
State income taxes, net of federal tax benefit, percent	(1.80%)	12.00%	3.20%
Effect of foreign income taxes, amount	$ 125	$ 406	$ 1,336
Effect of foreign income taxes, percent	0.40%	(4.40%)	1.40%
Excess tax depletion, amount	$ (10,535)	$ 0	$ (13,141)
Excess tax depletion, percent	(29.80%)	0.00%	(13.40%)
Uncertain tax positions, amount	$ 1,473	$ 0	$ 0
Uncertain tax positions, percent	4.20%	0.00%	0.00%
Compensation, amount	$ 3,192	$ 1,310	$ 1,799
Compensation, percent	9.00%	(14.20%)	1.80%
Valuation allowance, amount	$ (544)	$ 1,479	$ 1,400
Valuation allowance, percent	(1.50%)	(16.00%)	1.40%
Tax credits, amount	$ (210)	$ 1,150	$ (2,536)
Tax credits, percent	(0.60%)	(12.40%)	(2.60%)
Non-controlling interest, amount	$ 0	$ 726	$ (3,687)
Non-controlling interest, percent	0.00%	(7.90%)	(3.80%)
State rate change and prior period adjustments, amount	$ 642	$ 1,797	$ (4,565)
State rate change and prior period adjustments, percent	1.80%	(19.40%)	(4.60%)
Other, amount	$ 360	$ 154	$ 208
Other, percent	1.00%	(1.60%)	0.20%
Total Income Tax Expense	$ 1,297	$ 3,972	$ 4,539
Income Tax Expense / Effective Rate, percent	3.70%	(42.90%)	4.60%