Note 4 - Summary of Employees' Stock Options Activities (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 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	6 years 61 days	6 years 89 days
Granted (in shares)	135,000
Granted (in dollars per share)	$ 16.87
Exercised (in shares)	(15,181)
Exercised (in dollars per share)	$ 5.848
Forfeited (in shares)	(23,391)
Forfeited (in dollars per share)	$ 25.56
Options outstanding as of March 31, 2016 (in shares)	2,878,988	2,782,560
Options outstanding as of March 31, 2016 (in dollars per share)	$ 14.119	$ 14.026
Options outstanding as of March 31, 2016	$ 20,507	$ 21,337
Vested and expected to vest (in shares)	2,783,465
Vested and expected to vest (in dollars per share)	$ 11.971
Vested and expected to vest	$ 20,471
Vested and expected to vest	6 years 34 days
Options exercisable at the end of the year (in shares)	1,911,497
Options exercisable at the end of the year (in dollars per share)	$ 9.873
Options exercisable at the end of the year	$ 19,736
Options exercisable at the end of the year	5 years 6 days