Note 4 - Stockholders' Equity - Summary of Employees' Stock Options Activities (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Options outstanding (in shares)	2,388,348
Options outstanding (in dollars per share)	$ 15.243
Options outstanding	$ 37,625	$ 30,025
Options outstanding (Year)	5 years 251 days	5 years 314 days
Granted (in shares)
Granted (in dollars per share)
Exercised (in shares)	(126,070)
Exercised (in dollars per share)	$ 7.417
Forfeited (in shares)	(5,749)
Forfeited (in dollars per share)	$ 26.634
Options outstanding (in shares)	2,256,529	2,388,348
Options outstanding (in dollars per share)	$ 15.654	$ 15.243
Options exercisable at the end of the year (in shares)	1,750,759
Options exercisable at the end of the year (in dollars per share)	$ 13.536
Options exercisable at the end of the year	$ 32,869
Options exercisable at the end of the year (Year)	5 years 41 days