Note 6 - Employee Benefit Plans (Tables)

3 Months Ended

Mar. 31, 2020

Notes Tables

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

	Three Months Ended March 31,
	2020			2019
Expected life (in years)		1.25			1.25
Volatility		34.25	%		45.19	%
Risk-free interest rate		1.43	%		2.52	%
Expected dividend		—			—
Weighted average fair value of purchase rights granted during the period	$	4.83		$	3.67

	Three Months Ended March 31,
	2020			2019
Expected life (in years)		4.45			4.46
Volatility		38.77	%		45.26	%
Risk-free interest rate		0.88	%		2.55	%
Expected dividend		—			—
Weighted average fair value per share of options granted during the period	$	5.21		$	4.51

Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	Three Months Ended March 31,
	2020		2019
Costs of revenues	$	909	$	860
Research and development		1,455		1,718
Selling, general and administrative		1,004		898
Stock-based compensation expenses	$	3,368	$	3,476

Share-based Payment Arrangement, Option, Activity [Table Text Block]

						Weighted
				Weighted		Average
				Average		Remaining		Aggregate
	Number of			Exercise		Contractual		Intrinsic
	Options			Price per		Term		Value
	(in thousands)			Share		(years)		(in thousands)
Outstanding, January 1, 2020		745		$	10.64
Granted (weighted average fair value of $5.21 per share)		13		$	15.76
Exercised		(21	)	$	7.68
Canceled		(2	)	$	10.66
Expired		(9	)	$	8.86
Outstanding, March 31, 2020		726		$	10.84		4.44	$	1,566
Vested and expected to vest, March 31, 2020		713		$	10.79		4.35	$	1,560
Exercisable, March 31, 2020		562		$	10.10		3.18	$	1,484

Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block]

				Weighted
				Average Grant
	Shares			Date Fair Value
	(in thousands)			Per Share
Nonvested, January 1, 2020		1,887		$	12.30
Granted		248		$	15.35
Vested		(275	)	$	13.52
Forfeited		(26	)	$	11.78
Nonvested, March 31, 2020		1,834		$	12.54