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Fair Value Measurements and Disclosures - Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands | Sep. 29, 2018 | Dec. 30, 2017
--- | --- | ---
Assets: |  |
Total marketable securities | $ 76,835 | $ 82,130
Total | 78,519 | 82,386
Level 1 [Member] |  |
Assets: |  |
Total marketable securities | 0 | 0
Total | 1,684 | 256
Level 2 [Member] |  |
Assets: |  |
Total marketable securities | 76,835 | 82,130
Total | 76,835 | 82,130
Level 3 [Member] |  |
Assets: |  |
Total marketable securities | 0 | 0
Total | 0 | 0
Money market funds [Member] |  |
Assets: |  |
Total cash equivalents | 1,684 | 256
Money market funds [Member] | Level 1 [Member] |  |
Assets: |  |
Total cash equivalents | 1,684 | 256
Money market funds [Member] | Level 2 [Member] |  |
Assets: |  |
Total cash equivalents | 0 | 0
Money market funds [Member] | Level 3 [Member] |  |
Assets: |  |
Total cash equivalents | 0 | 0
U.S. Government agency debt securities [Member] |  |
Assets: |  |
Total marketable securities | 0 | 1,495
U.S. Government agency debt securities [Member] | Level 1 [Member] |  |
Assets: |  |
Total marketable securities | 0 | 0
U.S. Government agency debt securities [Member] | Level 2 [Member] |  |
Assets: |  |
Total marketable securities | 0 | 1,495
U.S. Government agency debt securities [Member] | Level 3 [Member] |  |
Assets: |  |
Total marketable securities | 0 | 0
Certificates of deposits [Member] |  |
Assets: |  |
Total marketable securities | 14,502 | 14,497
Certificates of deposits [Member] | Level 1 [Member] |  |
Assets: |  |
Total marketable securities | 0 | 0
Certificates of deposits [Member] | Level 2 [Member] |  |
Assets: |  |
Total marketable securities | 14,502 | 14,497
Certificates of deposits [Member] | Level 3 [Member] |  |
Assets: |  |
Total marketable securities | 0 | 0
Commercial paper [Member] |  |
Assets: |  |
Total marketable securities | 11,185 | 7,949
Commercial paper [Member] | Level 1 [Member] |  |
Assets: |  |
Total marketable securities | 0 | 0
Commercial paper [Member] | Level 2 [Member] |  |
Assets: |  |
Total marketable securities | 11,185 | 7,949
Commercial paper [Member] | Level 3 [Member] |  |
Assets: |  |
Total marketable securities | 0 | 0
Corporate debt securities [Member] |  |
Assets: |  |
Total marketable securities | 36,950 | 47,968
Corporate debt securities [Member] | Level 1 [Member] |  |
Assets: |  |
Total marketable securities | 0 | 0
Corporate debt securities [Member] | Level 2 [Member] |  |
Assets: |  |
Total marketable securities | 36,950 | 47,968
Corporate debt securities [Member] | Level 3 [Member] |  |
Assets: |  |
Total marketable securities | 0 | 0
Asset-backed Securities [Member] |  |
Assets: |  |
Total marketable securities | 14,198 | 10,221
Asset-backed Securities [Member] | Level 1 [Member] |  |
Assets: |  |
Total marketable securities | 0 | 0
Asset-backed Securities [Member] | Level 2 [Member] |  |
Assets: |  |
Total marketable securities | 14,198 | 10,221
Asset-backed Securities [Member] | Level 3 [Member] |  |
Assets: |  |
Total marketable securities | $ 0 | $ 0

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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
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