Note 12 - Shareholders' Equity - Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	132,000	76,000	0
Stock Option Plan 2001 [Member]
Options outstanding, Shares (in shares)	6,193	46,293	81,893
Options outstanding, Weighted average exercise price (in dollars per share)	$ 2.95	$ 2.95	$ 2.95
Options exercised, Shares (in shares)	(6,193)	(40,100)	(35,600)
Options exercised, Weighted average exercise price (in dollars per share)	$ 2.95	$ 2.95	$ 2.95
Options outstanding, Shares (in shares)		6,193	46,293
Options exercisable, Shares (in shares)
Expected to vest, Shares (in shares)
Options exercised, Shares (in shares)	(6,193)	(40,100)	(35,600)
Options outstanding, Weighted average exercise price (in dollars per share)		$ 2.95	$ 2.95
Stock Option Plan 2013 [Member]
Options outstanding, Shares (in shares)	196,500	160,600	192,800
Options outstanding, Weighted average exercise price (in dollars per share)	$ 13.84	$ 7.72	$ 7.60
Options exercised, Shares (in shares)	(23,715)	(33,600)	(25,000)
Options exercised, Weighted average exercise price (in dollars per share)	$ 7.10	$ 7.19	$ 6.65
Options outstanding, Shares (in shares)	302,385	196,500	160,600
Options exercisable, Shares (in shares)	96,660
Expected to vest, Shares (in shares)	182,293
Options cancelled, Shares (in shares)	(2,400)	(6,500)	(7,200)
Options cancelled, Weighted average exercise price (in dollars per share)	$ 8.75	$ 20.55	$ 8.14
Options exercised, Shares (in shares)	(23,715)	(33,600)	(25,000)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	132,000	76,000	0
Option granted, Weighted average exercise price (in dollars per share)	$ 21.45	$ 24.40
Options outstanding, Weighted average exercise price (in dollars per share)	$ 17.73	$ 13.84	$ 7.72
Options outstanding, Weighted average remaining contractual term in years (Year)	6 years
Options outstanding, Intrinsic value	$ 2,615,630
Options exercisable, Weighted average exercise price (in dollars per share)	$ 10.87
Options exercisable, Weighted average remaining contractual term in years (Year)	3 years 328 days
Options exercisable, Intrinsic value	$ 1,499,197
Expected to vest, Weighted average exercise price (in dollars per share)	$ 20.96
Expected to vest, Weighted average remaining contractual term in years (Year)	7 years
Expected to vest, Intrinsic value	$ 988,884