Note 4 - Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2017

Notes Tables

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,
	2017		2016		2017		2016
Cost of design-to-silicon yield-solutions	$	1,069	$	956	$	2,261	$	2,041
Research and development		848		651		1,682		1,357
Selling, general and administrative		987		684		1,845		1,559
Stock-based compensation expenses	$	2,904	$	2,291	$	5,788	$	4,957

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

	Three Months Ended June 30,						Six Months Ended June 30,
	2017			2016			2017			2016
Expected life (in years)		4.41			4.42			4.41			4.42
Volatility		41.63	%		43.58	%		41.53	%		44.26	%
Risk-free interest rate		1.67	%		1.30	%		1.69	%		1.25	%
Expected dividend		—			—			—			—
Weighted average fair value per share of options granted during the period	$	5.98		$	5.00		$	6.16		$	4.46

	Six Months Ended June 30 ,
	2017			2016
Expected life (in years)		1.25			1.25
Volatility		33.32	%		44.15	%
Risk-free interest rate		0.93	%		0.50	%
Expected dividend		—			—
Weighted average fair value per share of options granted during the period	$	6.78		$	3.56

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

	Number of Options (in thousands)			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term (years)		Aggregate Intrinsic Value (in thousands)
Outstanding, January 1, 2017		1,364		$	8.00
Granted (weighted average fair value of $ 6.16 per share)		96		$	17
Exercised		(257	)	$	7.04
Canceled		(3	)	$	17.80
Expired		-		$	-
Outstanding, June 30, 2017		1,200		$	8.89		4.78	$	9,288
Vested and expected to vest, June 30, 2017		1,182		$	8.78		4.71	$	9,271
Exercisable, June 30, 2017		989		$	7.42		3.86	$	9,010

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

	Shares (in thousands)			Weighted Average Grant Date Fair Value Per Share
Nonvested, January 1, 2017		1,542		$	15.50
Granted		751		$	16.56
Vested		(317	)	$	16.36
Forfeited		(20	)	$	15.70
Nonvested, June 30, 2017		1,956		$	15.76