Note 4 - Summary of Employees' Stock Options Activities (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 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	6 years 6 days	6 years 89 days
Granted (in shares)	135,000
Granted (in dollars per share)	$ 16.87
Exercised (in shares)	(142,494)
Exercised (in dollars per share)	$ 5.923
Forfeited (in shares)	(56,141)
Forfeited (in dollars per share)	$ 25.142
Options outstanding as of June 30, 2016 (in shares)	2,718,925	2,782,560
Options outstanding as of June 30, 2016 (in dollars per share)	$ 14.362	$ 14.026
Options outstanding as of June 30, 2016	$ 29,778	$ 21,337
Vested and expected to vest (in shares)	2,627,050
Vested and expected to vest (in dollars per share)	$ 12.354
Vested and expected to vest	$ 29,458
Vested and expected to vest	5 years 340 days
Options exercisable at the end of the year (in shares)	1,879,372
Options exercisable at the end of the year (in dollars per share)	$ 10.716
Options exercisable at the end of the year	$ 26,831
Options exercisable at the end of the year	5 years 7 days