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Revenue - Changes in Contract Assets and Contract Liabilities (Detail) - USD ($)
$ in Thousands
9 Months Ended
Sep. 26, 2020
Dec. 28, 2019
TFE    
Contract liabilities:    
Contract liabilities $ 1,450 $ 4,327
Contract liabilities:    
Change in contract liabilities (2,877)  
TFE | Accounts Receivable, Unbilled    
Contract assets:    
Contract assets 560 760
Contract assets:    
Change in contract assets (200)  
TFE | Deferred Revenue    
Contract liabilities:    
Contract liabilities 399 320
Contract liabilities:    
Change in contract liabilities 79  
TFE | Customer Advances    
Contract liabilities:    
Contract liabilities 1,051 4,007
Contract liabilities:    
Change in contract liabilities (2,956)  
Photonics    
Contract assets:    
Contract assets 3,361 3,309
Contract assets:    
Change in contract assets 52  
Photonics | Accounts Receivable, Unbilled    
Contract assets:    
Contract assets 3,238 3,210
Contract assets:    
Change in contract assets 28  
Photonics | Deferred Revenue    
Contract liabilities:    
Contract liabilities 31  
Contract liabilities:    
Change in contract liabilities 31  
Photonics | Retainage    
Contract assets:    
Contract assets 123 $ 99
Contract assets:    
Change in contract assets $ 24