Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Stock-based compensation costs
Stock based compensation costs	$ 12,119	$ 11,166	$ 24,311	$ 21,652
Income tax benefit	1,677	3,175	6,896	8,457
Share based compensation costs after tax	10,442	7,991	17,415	13,195
Total unrecognized compensation costs related to awards	84,900		$ 84,900
Weighted-average period of recognition of unrecognized compensation costs			2 years 2 months 12 days
Cost of revenues
Stock-based compensation costs
Stock based compensation costs	294	264	$ 590	522
Research and development
Stock-based compensation costs
Stock based compensation costs	5,669	5,503	11,438	10,750
Selling, general and administrative
Stock-based compensation costs
Stock based compensation costs	$ 6,156	$ 5,399	$ 12,283	$ 10,380

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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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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- Definition

Unrecognized cost of unvested share-based compensation awards.

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- Definition

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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