Note 7 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

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,
	2017		2016		2015
Cost of revenue	$	1,654	$	1,575	$	1,166
Research and development		14,816		14,041		11,156
Selling, general and administrative		36,147		29,373		29,241
Total stock-based compensation expense	$	52,617	$	44,989	$	41,563
Tax benefit related to stock-based compensation	$	5,054	$	-	$	-

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, 2015		589		$	28.48		1,659		$	28.11		1,800		$	23.57		4,048		$	26.14
Granted		271		$	49.82		927	(1)	$	47.61		-		$	-		1,198		$	48.11
Released		(319	)	$	26.56		(629	)	$	23.40		-		$	-		(948	)	$	24.47
Forfeited		(42	)	$	35.60		(24	)	$	28.68		-		$	-		(66	)	$	33.06
Outstanding at December 31, 2015		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
Released		(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
Released		(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

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, 2015		590		$	15.80		1.2	$	20,039
Exercised		(498	)	$	15.55
Forfeited and expired		(2	)	$	6.10
Outstanding at December 31, 2015		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
Exercisable at December 31, 2017		5		$	13.89		0.4	$	465

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

	Year Ended December 31,
	2017			2016			2015
Expected term (years)		0.5			0.5			0.5
Expected volatility		23.5	%		28.6	%		30.3	%
Risk-free interest rate		0.9	%		0.4	%		0.2	%
Dividend yield		0.9	%		1.2	%		1.4	%