Note 10 - Stockholders' Equity - Summary of Warrants and Options Issued to Employees and Directors (Details) - Employee Stock Options And Warrants [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance (in shares)	964,180	966,681	970,847
Balance, weighted average exercise price (in dollars per share)	$ 6.32	$ 6.32	$ 6.32
Balance, weighted average remaining contract life (Year)	3 years 233 days	4 years 204 days	5 years 200 days	6 years 197 days
Balance, aggregate intrinsic value			$ 751	$ 850
Exercised (in shares)		(2,001)	(2,333)
Exercised, weighted average exercise price (in dollars per share)		$ 5.70	$ 5.46
Exercised, aggregate intrinsic value			$ 4
Expired (in shares)	(40,282)	(500)	(1,833)
Expired, weighted average exercise price (in dollars per share)	$ 6.47	$ 4.58	$ 5.40
Balance (in shares)	923,898	964,180	966,681	970,847
Balance, weighted average exercise price (in dollars per share)	$ 6.32	$ 6.32	$ 6.32	$ 6.32
Exercisable (in shares)	923,898	964,180	966,681
Exercisable, weighted average exercise price (in dollars per share)	$ 6.32	$ 6.32	$ 6.32
Exercisable, weighted average remaining contract life (Year)	3 years 233 days	4 years 204 days	5 years 200 days
Exercisable, aggregate intrinsic value			$ 751