Note 12 - Stock Option Plans - Stock Option Activity (Details) - $ / shares	12 Months Ended		192 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018
Options outstanding at January 1 (in shares)	243,500	304,500
Options cancelled (in shares)	(8,000)	(18,000)	(266,680)
Options exercised (in shares)	(40,000)	(60,000)	(840,320)
Options granted (in shares)	12,000	17,000	1,314,500
Options outstanding at December 31 (in shares)	207,500	243,500	207,500
Options available for grant at December 31 (in shares)	805,000	817,000	805,000
Options exercisable at December 31 (in shares)	179,000	206,500	179,000
Granted (in dollars per share)	$ 7.80	$ 3.86
Exercised (in dollars per share)	2.79	1.63
Outstanding (in dollars per share)	2.33	2.17	$ 2.33
Exercisable at December 31 (in dollars per share)	1.82	1.87	1.82
Maximum [Member]
Granted (in dollars per share)		3.86
Exercised (in dollars per share)	3.89	1.72
Outstanding (in dollars per share)	7.80	3.89	7.80
Minimum [Member]
Exercised (in dollars per share)	0.69	1.52
Outstanding (in dollars per share)	$ 0.69	$ 0.69	$ 0.69