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Stock-Based Compensation - Weighted Average Grant-Date Fair Value of Stock Options and ESPP Purchases (Details) - $ / shares | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 29, 2018 | Jun. 30, 2017 | Jun. 29, 2018 | Jun. 30, 2017
Stock options |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Weighted average grant-date fair value (in dollars per share) | $ 9.82 | $ 10.07 | $ 10.37 | $ 10.01
ESPP |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Weighted average grant-date fair value (in dollars per share) | $ 6.84 | $ 5.65 | $ 7.17 | $ 4.61

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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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