Note 16 - Stock Based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Outstanding, beginning of year, shares (in shares)	4,979,475	3,861,650	3,005,825
Outstanding, beginning of year, weighted average exercise price (in dollars per share)	$ 6.05	$ 5.96	$ 4.98
Granted, number of shares (in shares)	1,270,450	1,356,500	1,106,800
Granted, weighted average exercise price (in dollars per share)	$ 2.98	$ 6.35	$ 8.34
Exercised, shares (in shares)	(17,000)	(53,550)	(174,850)
Exercise, weighted average exercise price (in dollars per share)	$ 2.43	$ 4.88	$ 3.83
Forfeited, shares (in shares)	(333,500)	(185,125)	(76,125)
Forfeited, weighted average exercise price (in dollars per share)	$ 5.34	$ 6.76	$ 6.80
Outstanding, end of year, shares (in shares)	5,899,425	4,979,475	3,861,650
Outstanding, end of year, weighted average exercise price (in dollars per share)	$ 5.44	$ 6.05	$ 5.96
Options exercisable at year-end, shares (in shares)	3,384,625	2,611,960	1,899,487
Options exercisable at year-end, weighted average exercise price (in dollars per share)	$ 5.67	$ 5.28	$ 4.53
Granted, Weighted-Average Grant Date Fair Value (in dollars per share)	$ 0.91	$ 2.15	$ 2.85