Note 11 - Share-based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Outstanding at beginning of year, weighted average exercise price (in dollars per share)	$ 1.96
Share-based Payment Arrangement, Option [Member]
Outstanding (in shares)	2,043,402	2,390,012
Outstanding at beginning of year, weighted average exercise price (in dollars per share)	$ 1.91	$ 1.85
Granted (in shares)	0	0
Granted, weighted average exercise price (in dollars per share)
Exercised (in shares)	(469,510)	(330,983)
Exercised, weighted average exercise price (in dollars per share)	$ 1.72	$ 1.36
Forfeited (in shares)	(3,437)	(15,627)
Forfeited, weighted average exercise price (in dollars per share)	$ 5.69	$ 4.34
Expired - vested (in shares)
Expired - vested, weighted average exercise price (in dollars per share)
Outstanding at end of year (in shares)	1,570,455	2,043,402
Outstanding at beginning of year, weighted average exercise price (in dollars per share)	$ 1.96	$ 1.91
Stock options exercisable at year end (in shares)	1,465,599	1,661,999
Stock options exercisable at year end, weighted average exercise price (in dollars per share)	$ 1.94	$ 1.87
Performance Shares [Member]
Outstanding (in shares)	964,997	999,997
Outstanding at beginning of year, weighted average exercise price (in dollars per share)	$ 1.64	$ 1.64
Granted (in shares)
Granted, weighted average exercise price (in dollars per share)
Exercised (in shares)	(227,500)	(35,000)
Exercised, weighted average exercise price (in dollars per share)	$ 1.64	$ 1.64
Outstanding at end of year (in shares)	737,497	964,997
Outstanding at beginning of year, weighted average exercise price (in dollars per share)	$ 1.64	$ 1.64
Stock options exercisable at year end (in shares)	737,497	465,001
Stock options exercisable at year end, weighted average exercise price (in dollars per share)	$ 1.64	$ 1.64