Note 4 - Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2016

Notes Tables

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Six Months Ended June 30, 2016
	(unaudited)
Expected dividend yield		0	%
Expected volatility		62	%
Risk-free interest rate		1.42	%
Expected term (years)		6.25

Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]

	Six Months Ended June 30, 2016 (unaudited)
	Number			Average exercise price		Aggregate intrinsic value (in thousands)		Average remaining contractual life (years)
Options outstanding as of January 1, 2016		2,782,560		$	14.026	$	21,337		6.246
Granted		135,000		$	16.870
Exercised		(142,494	)	$	5.923
Forfeited		(56,141	)	$	25.142
Options outstanding as of June 30, 2016		2,718,925		$	14.362	$	29,778		6.019
Vested and expected to vest		2,627,050		$	12.354	$	29,458		5.933
Options exercisable at the end of the period		1,879,372		$	10.716	$	26,831		5.020

Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block]

Range of exercise price			Options outstanding as of June 30, 2016		Weighted average remaining contractual life (years)		Weighted average exercise price		Options exercisable as of June 30, 2016		Weighted average remaining contractual life (years)		Weighted average exercise price of options exercisable
$0.901	-	$1.576		900,240		2.563	$	1.247		900,240		2.563	$	1.247
$6.230	-	8.800		116,243		5.389	$	6.834		116,243		5.389	$	6.834
$12.470	-	16.870		492,805		7.490	$	13.675		286,177		6.663	$	12.470
$19.510	-	21.660		583,615		8.117	$	21.208		264,672		8.034	$	21.203
$22.010	-	24.230		307,181		7.800	$	22.291		164,615		7.786	$	22.343
	$29.880			154,200		8.649	$	29.880		51,406		8.649	$	29.880
	$39.860			164,641		7.729	$	39.860		96,019		7.729	$	39.860
				2,718,925		6.019	$	14.362		1,879,372		5.020	$	10.716

Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]

	Options for shares of common stock		Exercise price per share		Options exercisable		Exercisable through
	(number)				(number)
February 2013		3,000	$	12.470		2,500	February 2023
August 2013		5,000	$	21.140		3,542	August 2023
October 2013		750	$	24.230		500	October 2023
March 2014		13,750	$	39.860		7,734	March 2024
May 2014		8,700	$	22.010		4,531	May 2024
November 2014		12,000	$	21.660		4,750	November 2024
May 2015		5,250	$	19.510		1,422	May 2025
February 2016		3,000	$	16.870		-	February 2026
		51,450				24,979

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]

	Number of shares underlying outstanding restricted stock units			Weighted- average grant date fair value
Unvested balance - January 1, 2016		643,506		$	23.38
Granted		829,744		$	17.37
Vested		(126,097	)	$	24.55
Forfeited		(25,600	)	$	18.88
Unvested balance – June 30, 2016		1,321,553		$	19.58

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]

	Three Months Ended June 30,				Six Months Ended June 30,
	2016		2015		2016		2015
	(unaudited)				(unaudited)
	(in thousands)				(in thousands)
Cost of revenues	$	172	$	111	$	318	$	202
Research and development		793		544		1,458		1,011
Sales and marketing		1,628		702		2,803		1,439
General and administrative		780		605		1,418		995
Total	$	3,373	$	1,962	$	5,997	$	3,647