| Interim Consolidated Financial Statement Details - Consolidated Balance Sheets (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sep. 27, 2020 | Dec. 29, 2019 | |||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Trade accounts receivable | $ 75,000 | $ 71,113 | ||||||||||
| Other receivables | 731 | 1,098 | ||||||||||
| Allowance for doubtful accounts | (2,325) | (2,292) | ||||||||||
| Total | 73,406 | 69,919 | ||||||||||
| Opening | 26,271 | 20,405 | ||||||||||
| Contract assets additions | 276,330 | 350,709 | ||||||||||
| Contract assets invoiced | (259,865) | (344,843) | ||||||||||
| Ending | 42,736 | 26,271 | ||||||||||
| Raw materials | 51,783 | 48,067 | ||||||||||
| Parts and other | 292 | 586 | ||||||||||
| Provision for obsolescence | (538) | (827) | ||||||||||
| Total | 51,537 | 47,826 | ||||||||||
| Property, plant and equipment | 74,005 | 72,614 | ||||||||||
| Accumulated depreciation, property, plant and equipment | (50,608) | (47,304) | ||||||||||
| Property, plant and equipment—net | 23,397 | 25,310 | ||||||||||
| Intangible assets | 21,000 | 21,000 | ||||||||||
| Intangible assets, accumulated amortization | (10,971) | (8,253) | ||||||||||
| Total amortization | 10,029 | 12,747 | ||||||||||
| Goodwill | 18,165 | 18,165 | ||||||||||
| Payroll | 7,515 | 5,504 | ||||||||||
| Deferred revenue | 5,915 | 0 | ||||||||||
| Professional services | 644 | 612 | ||||||||||
| Interest | 330 | 860 | ||||||||||
| Total | 23,125 | 11,164 | ||||||||||
| Customer Related [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Other accrued liabilities | 6,347 | 2,185 | ||||||||||
| Vendor Related [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Other accrued liabilities | 1,436 | 1,742 | ||||||||||
| Other Accrued Liabilities [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Other accrued liabilities | 938 | 261 | ||||||||||
| US [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Total amortization | 3,009 | 3,824 | ||||||||||
| Goodwill | 5,449 | 5,449 | ||||||||||
| Mexico [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Total amortization | 7,020 | 8,923 | ||||||||||
| Goodwill | 12,716 | 12,716 | ||||||||||
| Customer Relationships [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Intangible assets | 12,350 | 12,350 | ||||||||||
| Intangible assets, accumulated amortization | (2,340) | (1,414) | ||||||||||
| Order or Production Backlog [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Intangible assets | 6,990 | 6,990 | ||||||||||
| Intangible assets, accumulated amortization | (6,990) | (5,333) | ||||||||||
| Trade Names [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Intangible assets | 1,300 | 1,300 | ||||||||||
| Intangible assets, accumulated amortization | (1,300) | (1,300) | ||||||||||
| Noncompete Agreements [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Intangible assets | 360 | 360 | ||||||||||
| Intangible assets, accumulated amortization | (341) | (206) | ||||||||||
| Land [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Property, plant and equipment | 1,648 | 1,648 | ||||||||||
| Building [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Property, plant and equipment | [1] | 18,985 | 18,985 | |||||||||
| Accumulated depreciation, property, plant and equipment | [1] | (11,220) | (10,392) | |||||||||
| Machinery and Equipment [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Property, plant and equipment | [2],[3] | 44,116 | 42,732 | |||||||||
| Accumulated depreciation, property, plant and equipment | [2],[3] | (33,727) | (31,192) | |||||||||
| Furniture and Fixtures [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Property, plant and equipment | [2],[4] | 869 | 1,005 | |||||||||
| Accumulated depreciation, property, plant and equipment | [2],[4] | (423) | (546) | |||||||||
| Computer Equipment [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Property, plant and equipment | [2],[5] | 3,940 | 3,979 | |||||||||
| Accumulated depreciation, property, plant and equipment | [2],[5] | (3,162) | (3,289) | |||||||||
| Leasehold Improvements [Member] | ||||||||||||
| Condensed Balance Sheet Statements Captions [Line Items] | ||||||||||||
| Property, plant and equipment | [2] | 4,447 | 4,265 | |||||||||
| Accumulated depreciation, property, plant and equipment | [2] | $ (2,076) | $ (1,885) | |||||||||
| 
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