Note 8 - Summary of Stock Options - Summary of Option Activity Under All Plans (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($) $ / 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
Options outstanding, beginning of period	9 years 135 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | shares	129,267
Options granted (in dollars per share) | $ / shares	$ 6.35
Options exercised (in shares) | shares	(1,314)
Options exercised (in dollars per share) | $ / shares	$ 4.80
Options canceled (in shares) | shares	(18,380)
Options canceled (in dollars per share) | $ / shares	$ 8.55
Options outstanding, end of period (in shares) | shares	1,131,768
Options outstanding, end of period (in dollars per share) | $ / shares	$ 6.42
Options outstanding, end of period | $	$ 414,727
Vested and exercisable and expected to vest, end of period, Number Of Shares (in shares) | shares	1,035,338
Vested and exercisable and expected to vest, end of period, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 6.48
Vested and exercisable and expected to vest, end of period, Weighted Average Remaining Contractual Term	9 years 80 days
Vested and exercisable and expected to vest, end of period, Aggregate Intrinsic Value | $	$ 392,137
Vested and exercisable, end of period, Number Of Shares (in shares) | shares	179,832
Vested and exercisable, end of period, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 9.86
Vested and exercisable, end of period, Weighted Average Remaining Contractual Term	7 years 328 days
Vested and exercisable, end of period, Aggregate Intrinsic Value | $	$ 125,415