Note 10 - Stockholders' Equity - Summary of Warrants and Options Issued to Employees and Directors (Details) - Employee Stock Options And Warrants [Member] - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Balance (in shares)	923,898
Balance, weighted average exercise price (in dollars per share)	$ 6.32
Balance, weighted average remaining contract life (Year)	2 years 346 days	3 years 233 days
Balance, aggregate intrinsic value
Expired (in shares)	(74,263)
Expired, weighted average exercise price (in dollars per share)	$ 7.22
Balance (in shares)	849,635	923,898
Balance, weighted average exercise price (in dollars per share)	$ 6.24	$ 6.32
Exercisable (in shares)	849,635
Exercisable, weighted average exercise price (in dollars per share)	$ 6.24
Exercisable, weighted average remaining contract life (Year)	2 years 346 days
Exercisable, aggregate intrinsic value