Note 3 - Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

Notes Tables

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Cost of revenue	$	663	$	480	$	1,193	$	913
Research and development		5,412		4,194		9,841		8,188
Selling, general and administrative		16,634		11,218		27,685		21,820
Total stock-based compensation expense	$	22,709	$	15,892	$	38,719	$	30,921
Tax benefit related to stock-based compensation	$	706	$	829	$	1,544	$	1,959

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		44		$	140.59		440	(1)	$	103.02		-		$	-		484		$	106.41
Vested		(68	)	$	80.27		(485	)	$	55.36		(162	)	$	23.57		(715	)	$	50.52
Forfeited		(4	)	$	106.51		-		$	-		(4	)	$	68.48		(8	)	$	87.85
Outstanding at June 30, 2019		212		$	109.33		2,129		$	71.60		2,053		$	36.58		4,394		$	57.05

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

	Six Months Ended June 30,
	2019			2018
Expected term (in years)		0.5			0.5
Expected volatility		37.3	%		28.2	%
Risk-free interest rate		2.5	%		1.8	%
Dividend yield		1.2	%		1.0	%