Stock-Based Compensation Expense (Tables)

3 Months Ended

Mar. 30, 2014

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

The following table summarizes the Company’s stock option activity for the three-month period ended March 30, 2014:



	Shares (in thousands)		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2013	6,138		$	15.65
Granted	1,206		39.31
Exercised	(396	)	15.02
Forfeited or expired	(73	)	18.02
Outstanding as of March 30, 2014	6,875		$	19.80	7.4	$	98,435
Exercisable as of March 30, 2014	2,481		$	13.59	5.8	$	48,212
Options vested or expected to vest at March 30, 2014 (1)	6,130		$	18.93	7.2	$	92,123

(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 30, 2014		March 31, 2013
Risk-free rate	2.7	%	2.1	%
Expected dividend yield	—	%	—	%
Expected volatility	41	%	42	%
Expected term (in years)	5.4		5.9

Stock-Based Compensation Expense

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



	Three-months Ended
	March 30, 2014		March 31, 2013
Product cost of revenue	$	285	$	227
Service cost of revenue	63		63
Research, development, and engineering	1,056		813
Selling, general, and administrative	2,600		2,195
	$	4,004	$	3,298