Note 4 - Stockholders' Equity (Tables)

9 Months Ended

Sep. 30, 2018

Notes Tables

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Costs of Design-to-silicon-yield solutions	$	787	$	1,184	$	2,768	$	3,445
Research and development		725		877		2,449		2,558
Selling, general and administrative		756		888		2,608		2,734
Stock-based compensation expenses	$	2,268	$	2,949	$	7,825	$	8,737

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

	Three Months Ended September 30,						Nine Months Ended September 30,
	2018			2017			2018			2017
Expected life (in years)		4.43			4.41			4.43			4.41
Volatility		44.01	%		41.49	%		43.82	%		41.53	%
Risk-free interest rate		2.73	%		1.65	%		2.71	%		1.69	%
Expected dividend		-			-			-			-
Weighted average fair value per share of options granted during the period	$	4.21		$	5.78		$	4.22		$	6.14

	Nine Months Ended September 30,
	2018			2017
Expected life (in years)		1.25			1.25
Volatility		42.85	%		40.63	%
Risk-free interest rate		2.48	%		1.25	%
Expected dividend		—			—
Weighted average fair value per share of options granted during the period	$	3.62		$	5.22

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, 2018		1,045		$	9.65
Granted (weighted average fair value of $4.22 per share)		98		$	10.71
Exercised		(68	)	$	6.88
Canceled or expired		(30	)	$	13.84
Outstanding, September 30, 2018		1,045		$	9.81		4.64	$	1,422
Vested and expected to vest, September 30, 2018		1,039		$	9.77		4.59	$	1,422
Exercisable, September 30, 2018		806		$	8.60		3.31	$	1,422

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

	Shares (in thousands)			Weighted Average Grant Date Fair Value Per Share
Outstanding, January 1, 2018		1,617		$	15.66
Granted		113		$	10.70
Vested		(440	)	$	15.73
Forfeited		(116	)	$	15.21
Outstanding, September 30, 2018		1,174		$	15.21