Note 3 - Stock-based Compensation (Tables)

6 Months Ended

Jun. 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 June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Cost of revenue	$	480	$	452	$	913	$	810
Research and development		4,194		3,961		8,188		7,459
Selling, general and administrative		11,218		10,714		21,820		18,520
Total stock-based compensation expense	$	15,892	$	15,127	$	30,921	$	26,789
Tax benefit related to stock-based compensation	$	829	$	-	$	1,959	$	-

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, 2018		258		$	66.30		2,266		$	48.59		1,620	$	23.57		4,144		$	39.91
Granted		84		$	113.36		626	(1)	$	81.93		-	$	-		710		$	85.66
Vested		(92	)	$	58.40		(557	)	$	40.38		-	$	-		(649	)	$	42.94
Forfeited		(9	)	$	77.47		(5	)	$	60.20		-	$	-		(14	)	$	71.41
Outstanding at June 30, 2018		241		$	85.38		2,330		$	59.49		1,620	$	23.57		4,191		$	47.09

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

	Six Months Ended June 30,
	2018			2017
Expected term (years)		0.5			0.5
Expected volatility		28.2	%		23.4	%
Risk-free interest rate		1.8	%		0.7	%
Dividend yield		1.0	%		0.9	%