Note 4 - Stockholders' Equity - Summary of Employees' Stock Options Activities (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Options outstanding as of January 1, 2016 (in shares)	2,782,560
Options outstanding as of January 1, 2016 (in dollars per share)	$ 14.026
Options outstanding as of January 1, 2016	$ 21,337
Options outstanding as of January 1, 2016	5 years 338 days	6 years 89 days
Granted (in shares)	135,000
Granted (in dollars per share)	$ 16.87
Exercised (in shares)	(324,992)
Exercised (in dollars per share)	$ 6.661
Forfeited (in shares)	(75,834)
Forfeited (in dollars per share)	$ 26.334
Options outstanding as of September 30, 2016 (in shares)	2,516,734	2,782,560
Options outstanding as of September 30, 2016 (in dollars per share)	$ 14.759	$ 14.026
Options outstanding as of September 30, 2016	$ 40,122	$ 21,337
Vested and expected to vest (in shares)	2,444,514
Vested and expected to vest (in dollars per share)	$ 14.531
Vested and expected to vest	$ 39,511
Vested and expected to vest	5 years 312 days
Options exercisable at the end of the year (in shares)	1,784,407
Options exercisable at the end of the year (in dollars per share)	$ 11.569
Options exercisable at the end of the year	$ 34,033
Options exercisable at the end of the year	5 years 16 days