Note 10 - Stock-based Compensation - Stock Options Outstanding (Details) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($) $ / shares shares
Options, Exercisable, Number of Shares (in shares) | shares	2,392,065
Options, Exercisable, Weighted Average Exercise Price (in dollars per share) | $ / shares (in dollars per share) | $ / shares	$ 10.06
Options, Exercisable, Weighted Average Remaining Contractual Term (Year)	5 years 4 months 28 days
Options, Exercisable, Aggregate Intrinsic Value | $	$ 0.2
Options, Vested and Expected to Vest, Exercisable, Number of Shares (in shares) | shares	6,421,165
Options, Vested and Expected to Vest, Exercisable, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 4.91
Options, Vested and Expected to Vest, Exercisable, Weighted Average Remaining Contractual Term (Year)	5 years 10 months 17 days
Options, Vested or Expected to Vest, Aggregate Intrinsic Value | $	$ 0.4