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Stock-based Compensation (Tables)

12 Months Ended

Dec. 28, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Allocated Employee Stock-Based Compensation Expense

We allocated the stock-based compensation expense for our equity incentive plans and our 2000 Employee Stock Purchase Plan (ESPP) as follows (in thousands):

	Year Ended December 31,
	2018				2017				2016
Research and development	$	13,115			$	7,569			$	9,366
Selling, general and administrative	27,511				16,369				13,546
Total stock-based compensation	$	40,626			$	23,938			$	22,912

Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value

The weighted average grant-date fair value per share of stock options and ESPP purchases was as follows:

	Year Ended December 31,
	2018				2017				2016
Stock options	$	9.07			$	11.42			$	4.77
ESPP	$	6.40			$	6.00			$	2.17

Schedule of Fair Value of Employee Share-Based Payments Awards Stock Option Assumptions and Weighted Average Fair Values

The grant-date fair value of stock option grants and ESPP purchases was estimated using the following assumptions:

	Year Ended December 31,
	2018			2017			2016
Stock options:
Risk-free interest rate	2.81	%		1.98	%		1.15	%
Dividend yield	—	%		—	%		—	%
Volatility	55	%		59	%		76	%
Expected life	4.4 years			4.5 years			4.4 years
ESPP:
Risk-free interest rate	1.93	%		1.09	%		0.55	%
Dividend yield	—	%		—	%		—	%
Volatility	53	%		58	%		65	%
Expected life	6 months			6 months			6 months

Schedule of Fair Value of Employee Share-Based Payments Awards ESPP Assumptions and Weighted Average Fair Values

The grant-date fair value of stock option grants and ESPP purchases was estimated using the following assumptions:

	Year Ended December 31,
	2018			2017			2016
Stock options:
Risk-free interest rate	2.81	%		1.98	%		1.15	%
Dividend yield	—	%		—	%		—	%
Volatility	55	%		59	%		76	%
Expected life	4.4 years			4.5 years			4.4 years
ESPP:
Risk-free interest rate	1.93	%		1.09	%		0.55	%
Dividend yield	—	%		—	%		—	%
Volatility	53	%		58	%		65	%
Expected life	6 months			6 months			6 months

Summary of All Stock Option Activity

Activity for stock options during the year ended December 31, 2018 was as follows (dollars in thousands, except per share amounts):

	Shares			Weighted  Average Exercise Price				Weighted  Average Remaining Contractual Term		Aggregate Intrinsic Value
Stock options outstanding at December 31, 2017	22,208,446			$	6.83
Granted	3,238,473			$	19.40
Exercised	(2,466,579	)		$	4.90
Forfeited	(288,197	)		$	15.71
Expired	(18,081	)		$	20.64
Stock options outstanding at December 31, 2018	22,674,062			$	8.71			3.7 years		$	254,201
Exercisable at December 31, 2018	16,463,202			$	5.65			3.0 years		$	229,699

Summary of All RSU Activity

Activity for RSUs during the year ended December 31, 2018 was as follows (dollars in thousands, except per share amounts):

	Shares			Weighted  Average Grant Date Fair Value				Weighted  Average Remaining Contractual  Term		Aggregate Intrinsic Value
RSUs outstanding at December 31, 2017	3,762,990			$	17.76
Awarded	2,519,425			$	18.46
Vested and released	(1,081,339	)		$	16.05
Forfeited	(343,742	)		$	18.99
RSUs outstanding at December 31, 2018	4,857,334			$	18.42			2.1 years		$	94,427

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Tabular disclosure of the allocation of equity-based compensation costs to a given line item on the balance sheet and income statement for the period. This may include the reporting line for the costs and the amount capitalized and expensed.

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Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value.

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