Note 4 - Stockholders' Equity - Summary of Employees' Stock Options Activities (Details) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares
Options outstanding (in shares) | shares	2,388,348
Options outstanding (in dollars per share) | $ / shares	$ 15.243
Options outstanding (in dollars per share) | $ / shares	$ 15.941	$ 15.243
Options outstanding | $	$ 42,589	$ 30,025
Options outstanding (Year)	5 years 12 days	5 years 314 days
Options exercisable at the end of the year (in shares) | shares	1,633,271
Options exercisable at the end of the year (in dollars per share) | $ / shares	$ 14.216
Granted (in shares) | shares
Granted (in dollars per share) | $ / shares
Exercised (in shares) | shares	(330,351)
Exercised (in dollars per share) | $ / shares	$ 10.324
Forfeited (in shares) | shares	(72,893)
Forfeited (in dollars per share) | $ / shares	$ 18.148
Options outstanding (in shares) | shares	1,985,104	2,388,348
Options exercisable at the end of the year | $	$ 37,856
Options exercisable at the end of the year (Year)	4 years 227 days