Note 7 - Stock-based Compensation - Stock Option Activity (Details)	9 Months Ended
	Sep. 30, 2016 USD ($) $ / shares shares
Stock Option Plan 2001 [Member] | Employee Stock Option [Member]
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 2.95
Options outstanding, weighted average remaining contractual term	2 years 182 days
Options outstanding, intrinsic value | $	$ 751,000
Stock Option Plan 2001 [Member]
Options outstanding (in shares)	192,893
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 5.75
Options forfeited (in shares)	(55,800)
Options forfeited, weighted average exercise price (in dollars per share) | $ / shares	$ 12.61
Options exercised (in shares)	(34,000)
Options exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 2.95
Options outstanding (in shares)	103,093
Options exercisable at September 30, 2016 (in shares)	103,093
Options exercisable at September 30, 2016 (in dollars per share) | $ / shares	$ 2.95
Options exercisable, weighted average remaining contractual term	2 years 182 days
Options exercisable, intrinsic value | $	$ 751,000
Options granted (in shares)	55,800
Stock Option Plan 2013 [Member]
Options outstanding (in shares)	102,400
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 6.32
Options forfeited (in shares)	(108,000)
Options forfeited, weighted average exercise price (in dollars per share) | $ / shares	$ 8.75
Options exercised (in shares)	(6,800)
Options exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 6.32
Options outstanding (in shares)	203,600
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 7.61
Options outstanding, weighted average remaining contractual term	6 years 182 days
Options outstanding, intrinsic value | $	$ 535,000
Options exercisable at September 30, 2016 (in shares)	45,200
Options exercisable at September 30, 2016 (in dollars per share) | $ / shares	$ 6.32
Options exercisable, weighted average remaining contractual term	5 years 219 days
Options exercisable, intrinsic value | $	$ 177,000
Options granted (in shares)	108,000
Expected to vest (in shares)	138,172
Expected to vest, weighted average exercise price (in dollars per share) | $ / shares	$ 7.98
Expected to vest, weighted average remaining contractual term	6 years 292 days
Expected to vest, intrinsic value | $	$ 312,000