Note 4 - Income Taxes - Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Tax at federal statutory rate	21.00%	21.00%	21.00%
State taxes, net of federal	1.20%	3.60%	7.40%
Permanent items	5.80%	3.70%	30.60%
Other	(0.40%)	(0.70%)	(0.20%)
State rate change	(1.80%)	0.50%	(0.50%)
Valuation allowance	(26.40%)	(28.60%)	(58.80%)
Effective tax rate	(0.60%)	(0.50%)	(0.50%)