Note 8 - Summary of Stock Options - Summary of Option Activity Under All Plans (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016 USD ($) $ / shares shares	Dec. 31, 2015 $ / shares shares
Options outstanding, beginning of period (in shares) | shares	1,022,195
Options outstanding, beginning of period (in dollars per share) | $ / shares	$ 6.47
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	8 years 339 days	9 years 135 days
Options granted (in shares) | shares	378,932
Options granted (in dollars per share) | $ / shares	$ 7.25
Options exercised (in shares) | shares	(3,020)
Options exercised (in dollars per share) | $ / shares	$ 4.80
Options canceled (in shares) | shares	(82,299)
Options canceled (in dollars per share) | $ / shares	$ 7.55
Options outstanding, end of period (in shares) | shares	1,315,808	1,022,195
Options outstanding, end of period (in dollars per share) | $ / shares	$ 6.63	$ 6.47
Options outstanding, end of period | $	$ 1,615,644
Vested and exercisable and expected to vest, end of period, Number Of Shares (in shares) | shares	1,221,813
Vested and exercisable and expected to vest, end of period, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 6.65
Vested and exercisable and expected to vest, end of period, Weighted Average Remaining Contractual Term	8 years 328 days
Vested and exercisable and expected to vest, end of period, Aggregate Intrinsic Value | $	$ 1,523,776
Vested and exercisable, end of period, Number Of Shares (in shares) | shares	279,725
Vested and exercisable, end of period, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 8.05
Vested and exercisable, end of period, Weighted Average Remaining Contractual Term	7 years 306 days
Vested and exercisable, end of period, Aggregate Intrinsic Value | $	$ 473,807