Note 6 - Stock-based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2020
Outstanding at January 1, 2020 (in shares)	1,541,792
Outstanding at January 1, 2020, weighted average exercise price (in dollars per share)	$ 6.88
Granted (in shares)	256,000
Granted, weighted average exercise price (in dollars per share)	$ 6.51
Exercised (in shares)	(50,797)
Exercised, weighted average exercise price (in dollars per share)	$ 4.29
Forfeited or expired (in shares)	(17,584)
Forfeited or expired, weighted average exercise price (in dollars per share)	$ 7.72
Outstanding at September 30, 2020 (in shares)	1,729,411
Outstanding at March 31, 2020, weighted average exercise price (in dollars per share)	$ 6.89
Outstanding at March 31, 2020, weighted average remaining contractual term (Year)	3 years 21 days
Outstanding at March 31, 2020, aggregate intrinsic value	$ 745
Vested and Expected to Vest (in shares)	1,626,494
Options vested and expected to vest, weighted average exercise price (in dollars per share)	$ 6.84
Options vested and expected to vest, weighted average remaining contractual term (Year)	2 years 10 months 17 days
Options vested and expected to vest, aggregate intrinsic value	$ 745
Exercisable at September 30, 2020 (in shares)	1,244,119
Exercisable at March 31, 2020, weighted average exercise price (in dollars per share)	$ 6.63
Exercisable at March 31, 2020, weighted average remaining contractual term (Year)	1 year 11 months 1 day
Exercisable at March 31, 2020, aggregate intrinsic value	$ 745