Stock-Based Compensation Expense (Tables)

9 Months Ended

Sep. 29, 2019

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

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the nine-month period ended September 29, 2019:

	Shares (in thousands)		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2018	13,789		$	31.73
Granted	2,879		51.22
Exercised	(1,475	)	21.53
Forfeited or expired	(726	)	41.79
Outstanding as of September 29, 2019	14,467		$	36.14	7.19	$	203,774
Exercisable as of September 29, 2019	5,714		$	25.33	5.73	$	134,913
Options vested or expected to vest as of September 29, 2019 (1)	13,116		$	34.90	7.04	$	199,066

 (1) In addition to the vested options, the Company expects a portion of the unvested options to vest at some point in the future. Options expected to vest are calculated by applying an estimated forfeiture rate to the unvested options.

Weighted-Average Assumptions Used in Estimating Fair Values of Stock Options Granted

The fair values of stock options granted in each period presented were estimated using the following weighted-average assumptions:

	Three-months Ended				Nine-months Ended
	September 29, 2019		September 30, 2018		September 29, 2019		September 30, 2018
Risk-free rate	2.7	%	2.9	%	2.7	%	2.9	%
Expected dividend yield	0.39	%	0.32	%	0.39	%	0.32	%
Expected volatility	37	%	39	%	37	%	39	%
Expected term (in years)	5.1		5.4		5.2		5.3

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs

The following table presents the stock-based compensation expense by caption for each period presented on the Consolidated Statements of Operations (in thousands):

	Three-months Ended				Nine-months Ended
	September 29, 2019		September 30, 2018		September 29, 2019		September 30, 2018
Cost of revenue	$	334	$	544	$	1,114	$	1,898
Research, development, and engineering	3,616		3,197		11,633		11,166
Selling, general, and administrative	6,244		5,402		20,695		18,275
	$	10,194	$	9,143	$	33,442	$	31,339

Schedule of Nonvested Restricted Stock Units Activity

The following table summarizes the Company's RSUs activity for the nine-month period ended September 29, 2019:

	Shares (in thousands)	Weighted-Average Grant Date Fair Value
Nonvested as of December 31, 2018	—	$	—
Granted	75	45.20
Vested	—	—
Forfeited or expired	—	—
Nonvested as of September 29, 2019	75	$	45.20