Note 4 - Stockholders' Equity - Stock Options Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) $ / shares shares
Outstanding, January 1, 2017 (in shares) | shares	1,364
Outstanding, January 1, 2017 (in dollars per share) | $ / shares	$ 8
Granted (in shares) | shares	9
Granted (in dollars per share) | $ / shares	$ 21.94
Exercised (in shares) | shares	(89)
Exercised (in dollars per share) | $ / shares	$ 8.09
Canceled (in shares) | shares	(3)
Canceled (in dollars per share) | $ / shares	$ 17.73
Expired (in shares) | shares
Expired (in dollars per share) | $ / shares
Outstanding, March 31, 2017 (in shares) | shares	1,281
Outstanding, March 31, 2017 (in dollars per share) | $ / shares	$ 8.06
Outstanding, March 31, 2017 (Year)	4 years 102 days
Outstanding, March 31, 2017 | $	$ 18,659
Vested and expected to vest, March 31, 2017 (in shares) | shares	1,272
Vested and expected to vest, March 31, 2017 (in dollars per share) | $ / shares	$ 8.01
Vested and expected to vest, March 31, 2017 (Year)	4 years 91 days
Vested and expected to vest, March 31, 2017 | $	$ 18,592
Exercisable, March 31, 2017 (in shares) | shares	1,145
Exercisable, March 31, 2017 (in dollars per share) | $ / shares	$ 7.21
Exercisable, March 31, 2017 (Year)	3 years 266 days
Exercisable, March 31, 2017 | $	$ 17,639