Note 10 - Shareholders' Equity - Stock Option Valuation Assumptions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Exercise price (in dollars per share)	$ 3.83	$ 2.19
Risk-free interest rate	2.13%	1.13%
Expected volatility	58.38%	59.16%
Expected life in years (Year)	4 years 91 days	4 years 91 days
Dividend rate	0.00%
Black-Scholes fair value (in dollars per share)	$ 1.81	$ 1.03