Note 16 - Stock Based Compensation - Options Outstanding (Details)	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Options outstanding (in shares) | shares	5,899,425
Options outstanding, weighted-average exercise price (in dollars per share)	$ 5.44
Options exercisable (in shares) | shares	3,384,625
Options exercisable, weighted-average exercise price (in dollars per share)	$ 5.67
Range 1 [Member]
Lower range limit (in dollars per share)	1.55
Upper range limit (in dollars per share)	$ 3.53
Options outstanding (in shares) | shares	1,721,150
Options outstanding, weighted-average remaining contractual life (Year)	6 years 10 months 24 days
Options outstanding, weighted-average exercise price (in dollars per share)	$ 2.85
Options exercisable (in shares) | shares	507,200
Options exercisable, weighted-average exercise price (in dollars per share)	$ 2.53
Range 2 [Member]
Lower range limit (in dollars per share)	3.55
Upper range limit (in dollars per share)	$ 3.95
Options outstanding (in shares) | shares	595,725
Options outstanding, weighted-average remaining contractual life (Year)	3 years 9 months 18 days
Options outstanding, weighted-average exercise price (in dollars per share)	$ 3.60
Options exercisable (in shares) | shares	593,725
Options exercisable, weighted-average exercise price (in dollars per share)	$ 3.60
Range 3 [Member]
Lower range limit (in dollars per share)	3.99
Upper range limit (in dollars per share)	$ 7.85
Options outstanding (in shares) | shares	1,756,875
Options outstanding, weighted-average remaining contractual life (Year)	7 years 2 months 12 days
Options outstanding, weighted-average exercise price (in dollars per share)	$ 5.71
Options exercisable (in shares) | shares	1,025,875
Options exercisable, weighted-average exercise price (in dollars per share)	$ 5.31
Range 4 [Member]
Lower range limit (in dollars per share)	8.00
Upper range limit (in dollars per share)	$ 9.45
Options outstanding (in shares) | shares	1,825,675
Options outstanding, weighted-average remaining contractual life (Year)	6 years 8 months 12 days
Options outstanding, weighted-average exercise price (in dollars per share)	$ 8.22
Options exercisable (in shares) | shares	1,257,825
Options exercisable, weighted-average exercise price (in dollars per share)	$ 8.20