Note 12 - Stock Option Plans - Stock Options Outstanding and Exercisable (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number Outstanding (in shares)	207,500	243,500	304,500
Options Outstanding Exercise Price Range1 [Member]
Lower Range of Exercise Price (in dollars per share)	$ 0.69
Upper Range of Exercise Price (in dollars per share)	$ 1.72
Number Outstanding (in shares)	150,500
Wgt. Avg. Contractual Life Remaining (yrs) (Year)	3 years
Wgt. Avg. Exercise Price (in dollars per share)	$ 1.53
Aggregate Intrinsic Value	$ 1,714,670
Options Exercisable Exercise Price Range 1 [Member]
Lower Range of Exercise Price (in dollars per share)	$ 0.69
Upper Range of Exercise Price (in dollars per share)	$ 1.72
Exercisable Options (in shares)	150,500
Weighted-Average Contractual Life Remaining - Exercisable (Year)	3 years
Weighted-Average Exercise Price - Exercisable (in dollars per share)	$ 1.53
Aggregate Intrinsic Value - Exercisable	$ 1,714,670
Options Outstanding Exercise Price Range2 [Member]
Lower Range of Exercise Price (in dollars per share)	$ 2.97
Upper Range of Exercise Price (in dollars per share)	$ 7.80
Number Outstanding (in shares)	57,000
Wgt. Avg. Contractual Life Remaining (yrs) (Year)	7 years 328 days
Wgt. Avg. Exercise Price (in dollars per share)	$ 4.44
Aggregate Intrinsic Value	$ 483,120
Options Exercisable Exercise Price Range 2 [Member]
Lower Range of Exercise Price (in dollars per share)	$ 2.97
Upper Range of Exercise Price (in dollars per share)	$ 7.80
Exercisable Options (in shares)	28,500
Weighted-Average Contractual Life Remaining - Exercisable (Year)	7 years 109 days
Weighted-Average Exercise Price - Exercisable (in dollars per share)	$ 3.36
Aggregate Intrinsic Value - Exercisable	$ 272,490
Options Outstanding Exercise Price Range 3 [Member]
Lower Range of Exercise Price (in dollars per share)	$ 0.69
Upper Range of Exercise Price (in dollars per share)	$ 7.80
Number Outstanding (in shares)	207,500
Wgt. Avg. Contractual Life Remaining (yrs) (Year)	4 years 146 days
Wgt. Avg. Exercise Price (in dollars per share)	$ 2.33
Aggregate Intrinsic Value	$ 2,197,790
Options Exercisable Exercise Price Range3 [Member]
Lower Range of Exercise Price (in dollars per share)	$ 0.69
Upper Range of Exercise Price (in dollars per share)	$ 7.80
Exercisable Options (in shares)	179,000
Weighted-Average Contractual Life Remaining - Exercisable (Year)	3 years 255 days
Weighted-Average Exercise Price - Exercisable (in dollars per share)	$ 1.82
Aggregate Intrinsic Value - Exercisable	$ 1,987,160