Note 3 - Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2019

Notes Tables

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Cost of revenue	$	641	$	471	$	1,834	$	1,384
Research and development		4,960		3,979		14,801		12,168
Selling, general and administrative		15,699		10,393		43,384		32,213
Total stock-based compensation expense	$	21,300	$	14,843	$	60,019	$	45,765
Tax benefit related to stock-based compensation	$	595	$	764	$	2,139	$	2,723

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, 2019		240		$	95.38		2,174		$	61.61		2,219		$	35.69		4,633		$	50.94
Granted		47		$	141.03		535	(1)	$	98.45		-		$	-		582		$	101.89
Vested		(88	)	$	79.91		(571	)	$	54.41		(243	)	$	23.57		(902	)	$	48.61
Forfeited		(6	)	$	110.23		(43	)	$	42.72		(7	)	$	68.48		(56	)	$	53.06
Outstanding at September 30, 2019		193		$	113.22		2,095		$	73.37		1,969		$	37.08		4,257		$	58.38

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,
	2019			2018			2019			2018
Expected term (in years)		0.5			0.5			0.5			0.5
Expected volatility		36.7	%		30.8	%		37.0	%		29.5	%
Risk-free interest rate		1.9	%		2.2	%		2.2	%		2.0	%
Dividend yield		1.1	%		0.9	%		1.1	%		1.0	%