Note 9 - Stock-based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Outstanding at end of year (in dollars per share)	$ 2.00
Share-based Payment Arrangement, Option [Member]
Outstanding (in shares)	1,570,455	2,043,402
Outstanding, weighted average exercise price (in dollars per share)	$ 1.96	$ 1.91
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)	0	0
Granted, weighted average exercise price (in dollars per share)	$ 0	$ 0
Exercised (in shares)	(726,000)	(469,510)
Exercised, weighted average exercise price (in dollars per share)	$ 1.91	$ 1.72
Forfeited (in shares)	0	(3,437)
Forfeited, weighted average exercise price (in dollars per share)	$ 0	$ 5.69
Outstanding (in shares)	844,455	1,570,455
Outstanding at end of year (in dollars per share)	$ 2.00	$ 1.96
Options exercisable (in shares)	832,478	1,465,599
Options exercisable, weighted average exercise price (in dollars per share)	$ 1.98	$ 1.94
Performance Shares [Member]
Outstanding (in shares)	737,497	964,997
Outstanding, weighted average exercise price (in dollars per share)	$ 1.64	$ 1.64
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)	0	0
Granted, weighted average exercise price (in dollars per share)	$ 0	$ 0
Exercised (in shares)	(51,496)	(227,500)
Exercised, weighted average exercise price (in dollars per share)	$ 1.64	$ 1.64
Outstanding (in shares)	686,001	737,497
Outstanding at end of year (in dollars per share)	$ 1.64	$ 1.64
Options exercisable (in shares)	686,001	737,497
Options exercisable, weighted average exercise price (in dollars per share)	$ 1.64	$ 1.64