Goodwill - Summary of Changes in Carrying Amount of Goodwill (Details) $ in Thousands  | 
6 Months Ended | 
|---|---|
| 
 Jul. 01, 2017  
USD ($) 
 | |
| Goodwill [Roll Forward] | |
| Balance at beginning of period | $ 115,207 | 
| Acquisition | 1,804 | 
| Foreign Currency Translation | 554 | 
| Balance at end of period | 117,565 | 
| Operating Segments | Aerospace | |
| Goodwill [Roll Forward] | |
| Balance at beginning of period | 115,207 | 
| Acquisition | 1,804 | 
| Foreign Currency Translation | 554 | 
| Balance at end of period | 117,565 | 
| Operating Segments | Test Systems | |
| Goodwill [Roll Forward] | |
| Balance at beginning of period | 0 | 
| Acquisition | 0 | 
| Foreign Currency Translation | 0 | 
| Balance at end of period | $ 0 | 
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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. No definition available. 
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