Note 7 - Shareholders' Equity (Details Textual) - USD ($)		12 Months Ended
	Aug. 13, 2020	Dec. 31, 2020		Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)		135,000	[1]	781,500
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price (in dollars per share)		$ 1.89	[1]	$ 1.60
Treasury Stock, Common, Shares (in shares)		12,253,502		12,253,502
Treasury Stock, Value, Ending Balance		$ 18,929,915		$ 18,929,915
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.001	$ 0.001		$ 0.001
Open Market Sale Agreement [Member]
Sale of Stock, Authorized Offering Amount	$ 50,000,000.0
Sale of Stock, Percentage of Commissions Paid of Gross Proceeds From Sale Of Each Share	3.00%
Sale of Stock, Reimbursable Legal Expenses	$ 50,000
Sale of Stock, Termination Amount Under Agreement	$ 50,000,000.0
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)		135,000		645,671

[1] Represents the following stock options exercised: A total of 135,000 stock options exercised with a weighted average market price of $1.89.