Note 3 - Stock-based Compensation; Changes in Equity - Option Activity (Details)	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Outstanding, beginning of period (in shares) | shares	476,144
Outstanding, beginning of period (in dollars per share) | $ / shares	$ 3.97
Granted (in shares) | shares
Granted (in dollars per share) | $ / shares
Cancelled/Expired (in shares) | shares
Cancelled/Expired (in dollars per share) | $ / shares
Exercised/Issued (in shares) | shares	(5,000)
Exercised/Issued (in dollars per share) | $ / shares
Outstanding at the end of period (in shares) | shares	471,144
Outstanding at the end of period (in dollars per share) | $ / shares	$ 4.01
Exercisable at the end of period (in shares) | shares	157,639
Exercisable at the end of period (in dollars per share) | $ / shares	$ 4.84