Note 12 - Stock-based Compensation - Summary of Outstanding Options (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) $ / shares shares
Outstanding (in shares) | shares	3,121,200
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 3.50
Issued (in shares) | shares	50,000
Issued, weighted average exercise price (in dollars per share) | $ / shares	$ 3.13
Exercised (in shares) | shares	(419,500)
Exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 2.54
Cancelled/Forfeited (in shares) | shares
Cancelled/Forfeited, weighted average exercise price (in dollars per share) | $ / shares
Outstanding (in shares) | shares	2,751,700
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 3.64
Outstanding, weighted average remaining contractual life (Year)	2 years 328 days
Outstanding, aggregate intrinsic value | $	$ 934,117
Exercisable (in shares) | shares	959,868
Exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 3.34
Exercisable, weighted average remaining contractual life (Year)	2 years 36 days
Exercisable, aggregate intrinsic value | $	$ 239,953