Stock-Based Compensation Expense (Tables)

9 Months Ended

Sep. 27, 2020

Share-based Payment Arrangement [Abstract]

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the nine-month period ended September 27, 2020:

	Shares (in thousands)	Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2019	12,899	$	37.95
Granted	975	51.58
Exercised	(3,408)	26.82
Forfeited or expired	(529)	50.34
Outstanding as of September 27, 2020	9,937	$	42.45	7.03	$	191,245
Exercisable as of September 27, 2020	3,807	$	33.58	5.83	$	107,040
Options vested or expected to vest as of September 27, 2020 (1)	9,125	$	41.73	6.92	$	182,232

 (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 27, 2020		September 29, 2019		September 27, 2020		September 29, 2019
Risk-free rate	—	%	2.7	%	1.6	%	2.7	%
Expected dividend yield	—	%	0.39	%	0.43	%	0.39	%
Expected volatility	—	%	37	%	37	%	37	%
Expected term (in years)	—		5.1		6.0		5.2

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 27, 2020		September 29, 2019		September 27, 2020		September 29, 2019
Cost of revenue	$	324	$	334	$	1,041	$	1,114
Research, development, and engineering	2,815		3,616		10,582		11,633
Selling, general, and administrative	6,129		6,244		20,453		20,695
	$	9,268	$	10,194	$	32,076	$	33,442

Schedule of Nonvested Restricted Stock Units Activity

The following table summarizes the Company's RSUs activity for the nine-month period ended September 27, 2020:

	Shares (in thousands)	Weighted-Average Grant Date Fair Value
Nonvested as of December 31, 2019	150	$	48.63
Granted	438	51.73
Vested	—	—
Forfeited or expired	(34)	50.60
Nonvested as of September 27, 2020	554	$	50.96