Stock-Based Compensation Expense (Tables)

6 Months Ended

Jul. 01, 2018

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 six-month period ended July 1, 2018:

	Shares (in thousands)		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2017	12,726		$	25.24
Granted	2,119		56.03
Exercised	(881	)	16.82
Forfeited or expired	(373	)	32.68
Outstanding as of July 1, 2018	13,591		$	30.39	7.62	$	223,515
Exercisable as of July 1, 2018	4,781		$	19.98	6.17	$	117,767
Options vested or expected to vest as of July 1, 2018 (1)	12,177		$	29.20	7.49	$	210,965

 (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				Six-months Ended
	July 1, 2018		July 2, 2017		July 1, 2018		July 2, 2017
Risk-free rate	2.9	%	2.4	%	2.9	%	2.4	%
Expected dividend yield	0.32	%	0.39	%	0.32	%	0.39	%
Expected volatility	39	%	41	%	39	%	41	%
Expected term (in years)	5.4		5.2		5.3		5.3

Nonvested Restricted Stock Shares Activity

The following table summarizes the Company's restricted stock activity for the six-month period ended July 1, 2018:

	Shares (in thousands)		Weighted-Average Grant Fair Value		Aggregate Intrinsic Value (in thousands)
Nonvested as of December 31, 2017	20		$	17.03
Granted	—		—
Vested	(20	)	17.03		993
Forfeited or expired	—		—
Nonvested as of July 1, 2018	—		$	—	$	—

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				Six-months Ended
	July 1, 2018		July 2, 2017		July 1, 2018		July 2, 2017
Cost of revenue	$	557	$	454	$	1,354	$	884
Research, development, and engineering	3,154		2,715		7,969		5,325
Selling, general, and administrative	5,291		4,677		12,873		9,120
	$	9,002	$	7,846	$	22,196	$	15,329