| Inventories (Details) - USD ($) $ in Thousands | Dec. 28, 2019 | Dec. 29, 2018 | 
|---|---|---|
| Summary of inventories | ||
| Raw materials | $ 34,340 | $ 39,086 | 
| Work in process | 28,667 | 26,871 | 
| Finished goods | 29,711 | 23,963 | 
| Provision for obsolete and slow moving inventory | (7,523) | (3,931) | 
| Total | $ 85,195 | $ 85,989 | 
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- Definition Summary of inventories. No definition available. 
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- Definition Amount before valuation and LIFO reserves of completed merchandise or goods expected to be sold within one year or operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Amount before valuation and LIFO reserves of raw materials expected to be sold, or consumed within one year or operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Amount of valuation reserve for inventory. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Amount before valuation and LIFO reserves of merchandise or goods in the production process expected to be completed within one year or operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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