Note 3 - Stock-based Compensation (Tables)

3 Months Ended

Mar. 31, 2019

Notes Tables

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

	Three Months Ended March 31,
	2019		2018
Cost of revenue	$	531	$	433
Research and development		4,429		3,995
Selling, general and administrative		11,050		10,602
Total stock-based compensation expense	$	16,010	$	15,030
Tax benefit related to stock-based compensation	$	838	$	1,131

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		26		$	130.67		311	(1)	$	107.14		-		$	-		337		$	108.93
Vested		(33	)	$	77.83		(400	)	$	56.71		(81	)	$	23.57		(514	)	$	52.86
Forfeited		(2	)	$	89.22		-		$	-		(1	)	$	68.48		(3	)	$	83.26
Outstanding at March 31, 2019		231		$	101.91		2,085		$	69.34		2,137		$	36.14		4,453		$	55.09

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

	Three Months Ended March 31,
	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	%