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Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands | Mar. 27, 2019 | Dec. 27, 2018 | Dec. 26, 2018 | Dec. 28, 2017
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New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |
Operating lease liabilities | $ 101,224 | $ 101,300 |  |
Operating lease right-of-use assets | $ 94,249 | 94,100 | $ 0 |
Cumulative effect adjustment |  | (394) |  | $ (15,446)
(Deficit) [Member] |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |
Cumulative effect adjustment |  | (400) |  |
Deferred Tax Asset [Member] |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |
Cumulative effect adjustment |  | $ 100 |  |

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