Note 7 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Notes Tables

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]

	Year Ended December 31,
	2018		2017		2016
Cost of revenue	$	1,888	$	1,654	$	1,575
Research and development		15,990		14,816		14,041
Selling, general and administrative		42,729		36,147		29,373
Total stock-based compensation expense	$	60,607	$	52,617	$	44,989
Tax benefit related to stock-based compensation	$	4,383	$	5,054	$	-

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units 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, 2016		499		$	40.75		1,933			$	38.99		1,800		$	23.57		4,232		$	32.64
Granted		133		$	63.00		1,216		(1)	$	41.12		-		$	-		1,349		$	43.28
Vested		(239	)	$	36.43		(736	)		$	29.71		-		$	-		(975	)	$	31.36
Forfeited		(27	)	$	45.35		(129	)		$	36.82		(180	)	$	23.57		(336	)	$	30.38
Outstanding at December 31, 2016		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

Share-based Compensation, Stock Options, Activity [Table Text Block]

	Shares			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term		Aggregate Intrinsic Value
	(in thousands)					(in years)		(in thousands)
Outstanding at January 1, 2016		90		$	17.50		1.3	$	4,134
Exercised		(76	)	$	17.80
Outstanding at December 31, 2016		14		$	15.88		1.0	$	921
Exercised		(9	)	$	16.79
Outstanding at December 31, 2017		5		$	13.89		0.4	$	465
Exercised		(5	)	$	13.89
Outstanding at December 31, 2018		-		$	-		-	$	-

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

	Year Ended December 31,
	2018			2017			2016
Expected term (years)		0.5			0.5			0.5
Expected volatility		29.5	%		23.5	%		28.6	%
Risk-free interest rate		2.0	%		0.9	%		0.4	%
Dividend yield		1.0	%		0.9	%		1.2	%