Note 8 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

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

	Year Ended December 31,
	2019		2018		2017
Cost of revenue	$	2,409	$	1,888	$	1,654
Research and development		19,584		15,990		14,816
Selling, general and administrative		56,706		42,729		36,147
Total stock-based compensation expense	$	78,699	$	60,607	$	52,617
Tax benefit related to stock-based compensation	$	2,754	$	4,383	$	5,054

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, 2017		366		$	51.35		2,284		$	43.24		1,620		$	23.57		4,270		$	36.47
Granted		81		$	94.25		585	(1)	$	62.72		-		$	-		666		$	66.56
Vested		(175	)	$	48.35		(597	)	$	41.94		-		$	-		(772	)	$	43.39
Forfeited		(14	)	$	61.80		(6	)	$	49.82		-		$	-		(20	)	$	58.46
Outstanding at December 31, 2017		258		$	66.30		2,266		$	48.59		1,620		$	23.57		4,144		$	39.91
Granted		133		$	114.36		630	(1)	$	85.06		600		$	68.48		1,363		$	80.62
Vested		(136	)	$	60.23		(717	)	$	41.08		-		$	-		(853	)	$	44.13
Forfeited		(15	)	$	82.20		(5	)	$	63.16		(1	)	$	68.48		(21	)	$	76.92
Outstanding at December 31, 2018		240		$	95.38		2,174		$	61.61		2,219		$	35.69		4,633		$	50.94
Granted		52		$	141.32		512	(1)	$	99.88		-		$	-		564		$	103.68
Vested		(103	)	$	81.53		(656	)	$	53.72		(324	)	$	23.57		(1,083	)	$	47.34
Forfeited		(9	)	$	117.31		(43	)	$	42.72		(9	)	$	68.48		(61	)	$	57.01
Outstanding at December 31, 2019		180		$	115.45		1,987		$	74.50		1,886		$	37.63		4,053		$	59.16

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

	Year Ended December 31,
	2019			2018			2017
Expected term (in years)		0.5			0.5			0.5
Expected volatility		37.0	%		29.5	%		23.5	%
Risk-free interest rate		2.2	%		2.0	%		0.9	%
Dividend yield		1.1	%		1.0	%		0.9	%