Note 8 - Summary of Employees' Stock Options Activities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Options outstanding at the beginning of the year (in shares)	4,080,611	3,233,235	2,809,923
Options outstanding at the beginning of the year (in dollars per share)	$ 9.697	$ 4.033	$ 1.782
Options outstanding at the beginning of the year	$ 95,855	$ 65,723	$ 43,801
Options outstanding at the beginning of the year	6 years 89 days	6 years 33 days	5 years 255 days	5 years 347 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	191,200	1,111,940	541,150
Granted (in dollars per share)	$ 28.253	$ 25.077	$ 15.267
Exercised (in shares)	(1,334,351)	(213,174)	(105,021)
Exercised (in dollars per share)	$ 1.521	$ 1.663	$ 1.239
Forfeited (in shares)	(154,900)	(51,390)	(12,817)
Forfeited (in dollars per share)	$ 25.265	$ 19.449	$ 13.998
Options outstanding at the end of the year (in shares)	2,782,560	4,080,611	3,233,235	2,809,923
Options outstanding at the end of the year (in dollars per share)	$ 14.026	$ 9.697	$ 4.033	$ 1.782
Options outstanding at the end of the year	$ 21,337	$ 95,855	$ 65,723	$ 43,801
Vested and expected to vest (in shares)	2,677,503	3,965,741	3,203,465
Vested and expected to vest (in dollars per share)	$ 13.623	$ 9.318	$ 3.941
Vested and expected to vest	$ 21,284	$ 94,581	$ 65,412
Vested and expected to vest	6 years 56 days	6 years	5 years 243 days
Options exercisable at the end of the year (in shares)	1,794,249	2,620,454	2,550,694
Options exercisable at the end of the year (in dollars per share)	$ 8.841	$ 2.638	$ 1.473
Options exercisable at the end of the year	$ 20,496	$ 79,117	$ 58,377
Options exercisable at the end of the year	5 years 12 days	4 years 131 days	4 years 291 days