Note 3 - Stock-based Compensation - Summary of Stock Options (Details)	6 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares
Shares outstanding (in shares) | shares	244,500
Shares outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 2.17
Shares outstanding, weighted average remaining contractual life (Year)	5 years 182 days
Shares outstanding, aggregate intrinsic value | $	$ 341,000
Shares vested and exercisable (in shares) | shares	196,500
Shares vested and exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 1.76
Shares vested and exercisable, weighted average remaining contractual life (Year)	4 years 182 days
Shares vested and exercisable, aggregate intrinsic value | $	$ 341,000