Note 8 - Stockholders' Equity (Deficiency) - Summary of Employees' Stock Options Activities (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Options outstanding at the beginning of the year (in shares)	2,782,560	4,080,611	3,233,235
Options outstanding at the beginning of the year (in dollars per share)	$ 14.026	$ 9.697	$ 4.033
Options outstanding at the beginning of the year	$ 30,025	$ 21,337	$ 95,855	$ 65,723
Options outstanding at the beginning of the year (Year)	5 years 314 days	6 years 89 days	6 years 33 days	5 years 255 days
Granted (in shares)	135,000	191,200	1,111,940
Granted (in dollars per share)	$ 16.87	$ 28.253	$ 25.077
Exercised (in shares)	(445,535)	(1,334,351)	(213,174)
Exercised (in dollars per share)	$ 5.901	$ 1.521	$ 1.663
Forfeited (in shares)	(83,677)	(154,900)	(51,390)
Forfeited (in dollars per share)	$ 27.126	$ 25.265	$ 19.449
Options outstanding at the end of the period (in shares)	2,388,348	2,782,560	4,080,611	3,233,235
Options outstanding at the end of the period (in dollars per share)	$ 15.243	$ 14.026	$ 9.697	$ 4.033
Vested and expected to vest (in shares)	2,331,800	2,677,503	3,965,741
Vested and expected to vest (in dollars per share)	$ 15.074	$ 13.623	$ 9.318
Vested and expected to vest	$ 29,689	$ 21,284	$ 94,581
Vested and expected to vest (Year)	5 years 294 days	6 years 56 days	6 years
Options exercisable at the end of the year (in shares)	1,752,416	1,794,249	2,620,454
Options exercisable at the end of the year (in dollars per share)	$ 12.583	$ 8.841	$ 2.638
Options exercisable at the end of the year	$ 26,473	$ 20,496	$ 79,117
Options exercisable at the end of the year (Year)	5 years 43 days	5 years 12 days	4 years 131 days