Note 10 - Stock Compensation Plans - Summary of Stock Options (Details) - shares		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Options exercised (in shares)		67,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)		0	0
The 2003 Plan [Member]
Options exercised (in shares)	[1],[2]	67,500	0
Options expired (in shares)	[1],[2]	0	0
Options cancelled (in shares)	[1],[2]	0	0
All Plans [Member]
Options exercised (in shares)		1,014,820
Options cancelled (in shares)		282,680
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)		1,356,500
Options, vested and exercisable (in shares)		49,000
Options, non-vested (in shares)		10,000
The 2015 Plan [Member]
Options exercised (in shares)	[1],[3]	0	0
Options expired (in shares)	[1],[3]	0	0
Options cancelled (in shares)	[1],[3]	0	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)	[1],[3]	0	0
The Directors Plan [Member]
Options exercised (in shares)	[1],[4]	0	0
Options expired (in shares)	[1],[4]	0	0
Options cancelled (in shares)	[1],[4]	0	0
The 2011 Non-employee Director Stock Option Plan [Member]
Options exercised (in shares)	[1],[5]	0	0
Options expired (in shares)	[1],[5]	0	0
Options cancelled (in shares)	[1],[5]	0	0
The 2020 Non-employee Director Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)	[1],[6],[7]	4,443	4,380

[1] Indicates plans with stock options.

[2] The 2003 Stock Incentive Plan (the "2003 Plan") was instituted in March 2003. The 2003 Plan authorized the issuance of up to 450,000 options to purchase shares of common stock to officers and key employees, with vesting of such options occurring equally over a 3-year time period. In 2013, the 2003 Plan expired with 197,500 options ungranted.

[3] The 2015 Incentive Stock Plan (the "2015 Plan") was approved by shareholders in June 2015, which authorizes the issuance of up to 750,000 options to purchase shares of common stock to employees and key consultants and advisors.

[4] The Non-Employee Directors' Stock Option Plan (the "Directors Plan") was instituted in August 2000 that authorized the issuance of up to 200,000 options to purchase shares of common stock to non-employee directors. Upon adoption of the Directors Plan, each non-employee director was granted an option to acquire 5,000 shares. At each Annual Meeting, each director receives a grant of 4,000 options, which vest in 50% increments on the first and second anniversary. The Directors Plan expired in 2011, with 60,000 options ungranted.

[5] The 2011 Non-Employee Directors Stock Plan (the "2011 Directors Plan") was approved by shareholders in May 2011 with essentially the same terms and conditions as the Directors Plan.

[6] Indicates plans with stock grants.

[7] The 2020 Non-Employee Directors' Stock Incentive Plan (the "2020 Plan") was approved by shareholders in August 2020, which replaces the 2011 Director Plan and authorizes the issuance of 200,000 shares of common stock to non-employee directors. We expect to grant each independent director $50,000 of stock on the date of each subsequent Annual Meeting.