Note 8 - Summary of Stock Options - Summary of Options Outstanding and Exercisable (Details)	9 Months Ended
	Sep. 30, 2016 $ / shares shares
Range One [Member]
Options outstanding, weighted average exercise price (in dollars per share)	$ 2.64
Options outstanding, number (in shares) | shares	12,500
Options outstanding, weighted average remaining contractual term	8 years 226 days
Options exercisable, number exercisable (in shares) | shares	4,428
Options exercisable, weighted average exercise price (in dollars per share)	$ 2.64
Range Two [Member]
Options outstanding, weighted average exercise price (in dollars per share)	$ 3.75
Options outstanding, number (in shares) | shares	79,376
Options outstanding, weighted average remaining contractual term	8 years 131 days
Options exercisable, number exercisable (in shares) | shares	31,420
Options exercisable, weighted average exercise price (in dollars per share)	$ 3.75
Exercise price range, lower limit (in dollars per share)	3.68
Exercise price range, upper limit (in dollars per share)	3.76
Range Three [Member]
Options outstanding, weighted average exercise price (in dollars per share)	$ 4.80
Options outstanding, number (in shares) | shares	195,907
Options outstanding, weighted average remaining contractual term	7 years 321 days
Options exercisable, number exercisable (in shares) | shares	100,029
Options exercisable, weighted average exercise price (in dollars per share)	$ 4.80
Range Four [Member]
Options outstanding, weighted average exercise price (in dollars per share)	$ 6
Options outstanding, number (in shares) | shares	568,640
Options outstanding, weighted average remaining contractual term	9 years 62 days
Options exercisable, number exercisable (in shares) | shares	83,666
Options exercisable, weighted average exercise price (in dollars per share)	$ 6
Range Five [Member]
Options outstanding, weighted average exercise price (in dollars per share)	$ 6.35
Options outstanding, number (in shares) | shares	129,267
Options outstanding, weighted average remaining contractual term	9 years 146 days
Options exercisable, number exercisable (in shares) | shares
Options exercisable, weighted average exercise price (in dollars per share)
Exercise price range, lower limit (in dollars per share)	6.24
Exercise price range, upper limit (in dollars per share)	6.40
Range Six [Member]
Options outstanding, weighted average exercise price (in dollars per share)	$ 7.71
Options outstanding, number (in shares) | shares	284,203
Options outstanding, weighted average remaining contractual term	9 years 270 days
Options exercisable, number exercisable (in shares) | shares	14,267
Options exercisable, weighted average exercise price (in dollars per share)	$ 7.74
Exercise price range, lower limit (in dollars per share)	7
Exercise price range, upper limit (in dollars per share)	7.92
Range Seven [Member]
Options outstanding, weighted average exercise price (in dollars per share)	$ 9.92
Options outstanding, number (in shares) | shares	38,135
Options outstanding, weighted average remaining contractual term	6 years 51 days
Options exercisable, number exercisable (in shares) | shares	38,135
Options exercisable, weighted average exercise price (in dollars per share)	$ 9.92
Range Eight [Member]
Options outstanding, weighted average exercise price (in dollars per share)	$ 71.55
Options outstanding, number (in shares) | shares	5,902
Options outstanding, weighted average remaining contractual term	1 year 14 days
Options exercisable, number exercisable (in shares) | shares	5,902
Options exercisable, weighted average exercise price (in dollars per share)	$ 71.55
Exercise price range, lower limit (in dollars per share)	56
Exercise price range, upper limit (in dollars per share)	72
Range Nine [Member]
Options outstanding, weighted average exercise price (in dollars per share)	$ 118.68
Options outstanding, number (in shares) | shares	1,846
Options outstanding, weighted average remaining contractual term	1 year 83 days
Options exercisable, number exercisable (in shares) | shares	1,846
Options exercisable, weighted average exercise price (in dollars per share)	$ 118.68
Exercise price range, lower limit (in dollars per share)	96
Exercise price range, upper limit (in dollars per share)	149.04
Range Ten [Member]
Options outstanding, weighted average exercise price (in dollars per share)	$ 296
Options outstanding, number (in shares) | shares	32
Options outstanding, weighted average remaining contractual term	357 days
Options exercisable, number exercisable (in shares) | shares	32
Options exercisable, weighted average exercise price (in dollars per share)	$ 296
Options outstanding, weighted average exercise price (in dollars per share)	$ 6.63
Options outstanding, number (in shares) | shares	1,315,808
Options outstanding, weighted average remaining contractual term	8 years 339 days
Options exercisable, number exercisable (in shares) | shares	279,725
Options exercisable, weighted average exercise price (in dollars per share)	$ 8.05