Note 3 - Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2020

Notes Tables

Share-based Payment Arrangement, Cost by Plan [Table Text Block]

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
Cost of revenue	$	707	$	641	$	1,906	$	1,834
Research and development		5,334		4,960		14,666		14,801
Selling, general and administrative		16,934		15,699		46,009		43,384
Total stock-based compensation expense	$	22,975	$	21,300	$	62,581	$	60,019
Tax benefit related to stock-based compensation (1)	$	512	$	595	$	1,450	$	2,139

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

	Time-Based RSUs					PSUs and MPSUs					MSUs					Total
	Number of Shares			Weighted- Average Grant Date Fair Value Per Share		Number of Shares			Weighted- Average Grant Date Fair Value Per Share		Number of Shares			Weighted- Average Grant Date Fair Value Per Share		Number of Shares			Weighted- Average Grant Date Fair Value Per Share
Outstanding at January 1, 2020		180		$	115.45		1,987		$	74.50		1,886		$	37.63		4,053		$	59.16
Granted		73		$	184.19		622	(1)	$	172.83		-		$	-		695		$	174.03
Vested		(73	)	$	108.80		(1,136	)	$	58.21		(243	)	$	23.57		(1,452	)	$	54.98
Forfeited		(7	)	$	132.36		(10	)	$	84.95		(8	)	$	68.48		(25	)	$	92.50
Outstanding at September 30, 2020		173		$	146.72		1,463		$	128.96		1,635		$	39.57		3,271		$	85.19

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

	Three Months Ended September 30,						Nine Months Ended September 30,
	2020			2019			2020			2019
Expected term (in years)		0.5			0.5			0.5			0.5
Expected volatility		66.4	%		36.7	%		48.9	%		37.0	%
Risk-free interest rate		0.1	%		1.9	%		0.8	%		2.2	%
Dividend yield		0.7	%		1.1	%		0.9	%		1.1	%