Note 9 - Share-based compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
Common Class A [Member] | |||
Weighted average grant date fair value of stock options granted (in dollars per share) | $ 5.83 | $ 3.62 | $ 3.49 |
Exercised, aggregate intrinsic value | $ 2,681 | $ 459 | $ 350 |
Intrinsic value of stock options vested (in thousands) | $ 5,258 | $ 1,627 | $ 1,351 |
Common Class B [Member] | |||
Weighted average grant date fair value of stock options granted (in dollars per share) | $ 3.66 | $ 3.90 | $ 5.45 |
Exercised, aggregate intrinsic value | $ 202 | $ 632 | $ 151 |
Intrinsic value of stock options vested (in thousands) | $ 787 | $ 535 | $ 415 |