Employee Benefit Plans and Stock-based Compensation (Tables)

3 Months Ended

Mar. 30, 2018

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

Summary of Stock Options Outstanding

The following table summarizes the Company’s stock option activities and related information during the three months endedMarch 30, 2018 (in thousands, except per share amounts and terms):

	Stock Options Outstanding
	Number of Shares		Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value
Balance at December 31, 2017	3,880		$	6.04
Granted	—		—
Exercised	(78	)	3.02
Forfeited	(35	)	4.76
Canceled or expired	(502	)	8.88
Balance at March 30, 2018	3,265		$	5.69	3.0	$	556.3
As of March 30, 2018
Vested and expected to vest	3,244		$	5.70	3.0	$	548.1
Exercisable	2,910		$	5.80	2.8	$	417.7

Summary of Restricted Stock Units Outstanding

The following table summarizes the Company’s RSUs activities and related information as of March 30, 2018 (in thousands, except per share amounts and terms):

	Restricted Stock Units Outstanding
	Number of Shares		Weighted Average Grant Date Fair Value Per Share
Balance at December 31, 2017	2,904		$	5.09
Granted	2,198		3.77
Vested	(1,970	)	4.66
Forfeited	(135	)	5.42
Balance at March 30, 2018	2,997		$	4.39

Schedule of Defined Benefit Plans Obligations

The table below presents the components of net periodic benefit costs (in thousands):

	Three months ended
	March 30, 2018		March 31, 2017
Service cost	$	63	$	55
Interest cost	19		16
Recognized net actuarial loss	—		1
Net periodic benefit cost	$	82	$	72

Summary of Stock-Based Compensation Expense

Stock-based Compensation

The following table summarizes stock-based compensation for all plans (in thousands):

	Three months ended
	March 30, 2018		March 31, 2017
Stock-based compensation in:
Cost of revenue	$	515	$	445
Research and development expense	1,804		977
Selling, general and administrative expense	3,438		1,829
Total stock-based compensation in operating expense	5,242		2,806
Total stock-based compensation	$	5,757	$	3,251

Valuation Assumptions for Stock Options

	Stock Options
	Three months ended
	March 31, 2017
Expected term (years)	4.3
Volatility	42%
Risk-free interest rate	1.8%
Expected dividends	0.0%

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions

	ESPP Purchase Period Ending
	July 2, 2018		July 3, 2017
Expected term (years)	0.5		0.5
Volatility	60	%	63	%
Risk-free interest rate	1.7	%	0.8	%
Expected dividends	0.0	%	0.0	%
Estimated weighted average fair value per share at purchase date	$1.34		$1.71