Note 10 - Shareholders' Equity - Information About Stock Options (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Range of exercise prices, lower limit (in dollars per share)	$ 1.51
Range of exercise prices, upper limit (in dollars per share)	$ 3.90
Options outstanding options (in shares) | shares	884,998
Options outstanding weighted average exercise price (in dollars per share)	$ 2.26
Options outstanding weighted average remaining contract life (Year)	3 years 332 days
Options outstanding aggregate intrinsic value | $	$ 1,541,000
Options exercisable options (in shares) | shares	333,334
Options exercisable weighted average exercise price (in dollars per share)	$ 1.98
Options exercisable weighted average remaining contract life (Year)	3 years 69 days
Options exercisable aggregate intrinsic value | $	$ 673,000