Note 3 - Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2018

Notes Tables

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Cost of revenue	$	471	$	453	$	1,384	$	1,264
Research and development		3,979		3,838		12,168		11,297
Selling, general and administrative		10,393		9,678		32,213		28,198
Total stock-based compensation expense	$	14,843	$	13,969	$	45,765	$	40,759
Tax benefit related to stock-based compensation	$	764	$	-	$	2,723	$	-

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units 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, 2018		258		$	66.30		2,266		$	48.59		1,620	$	23.57		4,144		$	39.91
Granted		93		$	116.01		595	(1)	$	82.64		-	$	-		688		$	87.16
Vested		(121	)	$	59.01		(636	)	$	40.78		-	$	-		(757	)	$	43.69
Forfeited		(14	)	$	82.08		(6	)	$	63.16		-	$	-		(20	)	$	76.57
Outstanding at September 30, 2018		216		$	90.79		2,219		$	59.92		1,620	$	23.57		4,055		$	47.04

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,
	2018			2017			2018			2017
Expected term (years)		0.5			0.5			0.5			0.5
Expected volatility		30.8	%		23.5	%		29.5	%		23.5	%
Risk-free interest rate		2.2	%		1.2	%		2.0	%		0.9	%
Dividend yield		0.9	%		0.8	%		1.0	%		0.9	%