Stock-Based Compensation Expense (Tables)

3 Months Ended

Mar. 29, 2020

Share-based Payment Arrangement [Abstract]

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the three-month period ended March 29, 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	883		50.94
Exercised	(463	)	21.52
Forfeited or expired	(83	)	50.10
Outstanding as of March 29, 2020	13,236		$	39.32	7.12	$	113,087
Exercisable as of March 29. 2020	6,652		$	30.93	6.01	$	98,637
Options vested or expected to vest as of March 29, 2020 (1)	12,139		$	38.37	6.98	$	112,251

 (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
	March 29, 2020		March 31, 2019
Risk-free rate	1.6	%	2.7	%
Expected dividend yield	0.43	%	0.39	%
Expected volatility	37	%	37	%
Expected term (in years)	6.0		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
	March 29, 2020		March 31, 2019
Cost of revenue	$	354	$	451
Research, development, and engineering	5,366		4,467
Selling, general, and administrative	9,070		7,363
	$	14,790	$	12,281

Schedule of Nonvested Restricted Stock Units Activity

The following table summarizes the Company's RSUs activity for the three-month period ended March 29, 2020:

	Shares (in thousands)		Weighted-Average Grant Date Fair Value
Nonvested as of December 31, 2019	150		$	48.63
Granted	390		50.94
Vested	—		—
Forfeited or expired	(4	)	50.28
Nonvested as of March 29, 2020	536		$	50.30