Note 2 - Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2017

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,
	2017		2016		2017		2016
Cost of revenue	$	453	$	403	$	1,264	$	1,217
Research and development		3,838		3,986		11,297		11,001
Selling, general and administrative		9,678		9,127		28,198		22,023
Total	$	13,969	$	13,516	$	40,759	$	34,241

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]

	Time-Based RSUs			Weighted-Average Grant Date Fair Value Per Share		PSUs and MPSUs			Weighted-Average Grant Date Fair Value Per Share		MSUs		Weighted-Average Grant Date Fair Value Per Share		Total			Weighted-Average Grant Date Fair Value Per Share
Outstanding at January 1, 2017		366		$	51.35		2,284		$	43.24		1,620	$	23.57		4,270		$	36.47
Granted		75		$	92.53		645	(1)	$	61.08		-	$	-		720		$	64.35
Released		(148	)	$	47.93		(520	)	$	42.34		-	$	-		(668	)	$	43.57
Forfeited		(14	)	$	62.01		(5	)	$	49.82		-	$	-		(19	)	$	58.43
Outstanding at September 30, 2017		279		$	63.68		2,404		$	48.20		1,620	$	23.57		4,303		$	39.93

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,
	2017			2016			2017			2016
Expected term (years)		0.5			0.5			0.5			0.5
Expected volatility		23.5	%		27.5	%		23.5	%		28.6	%
Risk-free interest rate		1.2	%		0.5	%		0.9	%		0.4	%
Dividend yield		0.8	%		1.1	%		0.9	%		1.2	%