Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Stock-based compensation costs
Stock based compensation costs	$ 12,582	$ 11,355	$ 36,893	$ 33,007
Income tax benefit	619	2,674	7,515	11,131
Share based compensation costs after tax	11,963	8,681	29,378	21,876
Total unrecognized compensation costs related to awards	77,400		$ 77,400
Weighted-average period of recognition of unrecognized compensation costs			2 years 1 month 6 days
Cost of revenues
Stock-based compensation costs
Stock based compensation costs	324	281	$ 914	803
Research and development
Stock-based compensation costs
Stock based compensation costs	6,016	5,411	17,454	16,161
Selling, general and administrative
Stock-based compensation costs
Stock based compensation costs	$ 6,242	$ 5,663	$ 18,525	$ 16,043

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The amount of expense, net of income tax, recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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