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Summary of Significant Accounting Policies (Narratives) (Details) - USD ($) $ in Thousands |  | 3 Months Ended | 6 Months Ended
--- | --- | --- | ---
Jul. 01, 2018 | Dec. 31, 2017 | Dec. 31, 2017
Significant Accounting Policies [Line Items] |  |  |
Change in unrealized gains on available for sale securities |  | $ 54 | $ 237
ASU 2016-01 |  |  |
Significant Accounting Policies [Line Items] |  |  |
Change in unrealized gains on available for sale securities | $ 500 |  |

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- Definition Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669646-108580 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=114867106&loc=d3e637-108580 + Details
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