Note 8 - Share-based Compensation - Stock Option Activity (Details) - $ / shares	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement, Option [Member]
Outstanding (in shares)	844,455
Outstanding, weighted average exercise price (in dollars per share)	$ 2.00
Exercised (in shares)	(131,590)
Exercised, weighted average exercise price (in dollars per share)	$ 1.48
Forfeited (in shares)	(1,146)
Forfeited, weighted average exercise price (in dollars per share)	$ 5.69
Expired (in shares)	(35,714)
Expired, weighted average exercise price (in dollars per share)	$ 1.73
Outstanding (in shares)	676,005
Outstanding as of September 30, 2021 (in dollars per share)	$ 2.12
Options exercisable (in shares)	671,964
Options exercisable, weighted average exercise price (in dollars per share)	$ 2.11
Performance Shares [Member]
Outstanding (in shares)	686,001
Outstanding, weighted average exercise price (in dollars per share)	$ 1.64
Exercised (in shares)	(501,075)
Exercised, weighted average exercise price (in dollars per share)	$ 1.64
Outstanding (in shares)	184,926
Outstanding as of September 30, 2021 (in dollars per share)	$ 1.64
Options exercisable (in shares)	184,926
Options exercisable, weighted average exercise price (in dollars per share)	$ 1.64