Contract Liabilities (Tables)  | 
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 29, 2018  | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Revenue from Contract with Customer [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Disaggregation of Revenue | 
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| Contract with Customer, Asset and Liability | 
 The following table shows the changes in contract liability balances relating to prepaid supply agreements during 2018: 
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| X | ||||||||||
- Definition Tabular disclosure of contract balances and changes in contract balances. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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| X | ||||||||||
- Definition Tabular disclosure of disaggregation of revenue into categories depicting how nature, amount, timing, and uncertainty of revenue and cash flows are affected by economic factor. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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| X | ||||||||||
- References No definition available. 
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