Note 10 - Stock Option Plans - Stock Options Outstanding and Exercisable (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Number Outstanding (in shares)	126,500	207,500	243,500
Options Outstanding Exercise Price Range1 [Member]
Lower Range of Exercise Price (in dollars per share)	$ 1.52
Upper Range of Exercise Price (in dollars per share)	$ 1.72
Number Outstanding (in shares)	67,500
Wgt. Avg. Contractual Life Remaining (yrs) (Year)	1 year 182 days
Wgt. Avg. Exercise Price (in dollars per share)	$ 1.59
Aggregate Intrinsic Value	$ 2,588,850
Options Exercisable Exercise Price Range 1 [Member]
Lower Range of Exercise Price (in dollars per share)	$ 1.52
Upper Range of Exercise Price (in dollars per share)	$ 1.72
Exercisable Options (in shares)	67,500
Weighted-Average Contractual Life Remaining - Exercisable (Year)	1 year 182 days
Weighted-Average Exercise Price - Exercisable (in dollars per share)	$ 1.59
Aggregate Intrinsic Value - Exercisable	$ 2,588,850
Options Outstanding Exercise Price Range2 [Member]
Lower Range of Exercise Price (in dollars per share)	$ 3.50
Upper Range of Exercise Price (in dollars per share)	$ 39.11
Number Outstanding (in shares)	59,000
Wgt. Avg. Contractual Life Remaining (yrs) (Year)	8 years 219 days
Wgt. Avg. Exercise Price (in dollars per share)	$ 17.35
Aggregate Intrinsic Value	$ 1,332,740
Options Exercisable Exercise Price Range 2 [Member]
Lower Range of Exercise Price (in dollars per share)	$ 3.50
Upper Range of Exercise Price (in dollars per share)	$ 7.80
Exercisable Options (in shares)	17,000
Weighted-Average Contractual Life Remaining - Exercisable (Year)	7 years 182 days
Weighted-Average Exercise Price - Exercisable (in dollars per share)	$ 4.70
Aggregate Intrinsic Value - Exercisable	$ 599,040
Options Outstanding Exercise Price Range 3 [Member]
Lower Range of Exercise Price (in dollars per share)	$ 1.52
Upper Range of Exercise Price (in dollars per share)	$ 39.11
Number Outstanding (in shares)	126,500
Wgt. Avg. Contractual Life Remaining (yrs) (Year)	4 years 292 days
Wgt. Avg. Exercise Price (in dollars per share)	$ 8.94
Aggregate Intrinsic Value	$ 3,921,590
Options Exercisable Exercise Price Range3 [Member]
Lower Range of Exercise Price (in dollars per share)	$ 1.52
Upper Range of Exercise Price (in dollars per share)	$ 7.80
Exercisable Options (in shares)	84,500
Weighted-Average Contractual Life Remaining - Exercisable (Year)	2 years 255 days
Weighted-Average Exercise Price - Exercisable (in dollars per share)	$ 2.21
Aggregate Intrinsic Value - Exercisable	$ 3,187,890