Note 4 - Stock-based Compensation - Summary of Stock Option Activity (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Outstanding, weighted average exercise price (in dollars per share)	$ 5.14	$ 5.17
Outstanding, number of shares (in shares)	56,400	68,400
Cancelled, weighted average exercise price (in dollars per share)
Cancelled, number of shares (in shares)
Outstanding, weighted average exercise price (in dollars per share)	$ 5.14	$ 5.17
Outstanding, number of shares (in shares)	56,400	68,400
Outstanding, weighted average remaining contractual term (Year)	4 years 87 days	5 years 87 days
Outstanding, aggregate intrinsic value	$ 172,584	$ 83,933
Exercisable, weighted average exercise price (in dollars per share)	$ 5.14	$ 5.17
Exercisable, number of shares (in shares)	56,400	68,400
Exercisable, weighted average remaining contractual term (Year)	4 years 87 days	5 years 87 days
Exercisable, aggregate intrinsic value	$ 172,584	$ 83,933