Note 8 - EMPLOYEE BENEFIT PLANS (Tables)

9 Months Ended

Sep. 30, 2021

Notes Tables

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

	2021 Purchase Plan			2010 Purchase Plan
	Nine Months Ended September 30,			Nine Months Ended September 30,
	2021			2021			2020
Expected life (in years)		1.25			1.25			1.25
Volatility		48.00	%		34.25	%		34.25	%
Risk-free interest rate		0.11	%		1.43	%		1.43	%
Expected dividend		—			—			—
Weighted average fair value of purchase rights granted during the period	$	6.71		$	4.83		$	4.83

	Three Months Ended September 30,						Nine Months Ended September 30,
	2021			2020			2021			2020
Expected life (in years)		—			4.45			—			4.45
Volatility		—	%		43.92	%		—	%		40.90	%
Risk-free interest rate		—	%		0.23	%		—	%		0.60	%
Expected dividend		—			—			—			—
Weighted average fair value per share of options granted during the period	$	—		$	6.92		$	—		$	5.75

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

Stock-based compensation is estimated at the grant date based on the award’s fair value and is recognized on a straight-line basis over the vesting periods, generally four years. Stock-based compensation expense before taxes related to the Company’s stock plans and employee stock purchase plan was allocated as follows (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Costs of revenues	$	670	$	790	$	1,860	$	2,582
Research and development		1,299		1,148		4,013		3,613
Selling, general and administrative		1,394		1,192		3,601		3,281
Stock-based compensation expenses (1)	$	3,363	$	3,130	$	9,474	$	9,476

(1) The stock-based compensation expense during the three and nine months ended September 30, 2020, includes immaterial expense or credit adjustments related to cash-settled SARs granted to certain employees. The Company accounted for these awards as liability awards and the amount was included in accrued compensation and related benefits. All remaining outstanding SARs were fully exercised in the third quarter of 2020.

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

				Weighted
		Weighted		Average
		Average		Remaining	Aggregate
	Number of	Exercise		Contractual	Intrinsic
	Options (in	Price		Term	Value (in
	thousands)	per Share		(Years)	thousands)
Outstanding, January 1, 2021	456	$	10.95
Granted	—		—
Exercised	(160)		7.80
Canceled	(3)		13.52
Expired	(4)		6.90
Outstanding, September 30, 2021	289	$	12.72	3.30	$	2,983
Vested and expected to vest, September 30, 2021	286	$	12.69	3.25	$	2,956
Exercisable, September 30, 2021	240	$	12.27	2.43	$	2,590

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

		Weighted
		Average Grant
	Shares	Date Fair Value
	(in thousands)	Per Share
Non-vested, January 1, 2021	1,747	$	16.33
Granted	894	$	18.42
Vested	(579)	$	16.08
Forfeited	(81)	$	16.85
Non-vested, September 30, 2021	1,981	$	17.33