Quarterly report pursuant to Section 13 or 15(d)

Revenue - Disaggregated Revenue by Product Line (Details)

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Revenue - Disaggregated Revenue by Product Line (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Apr. 01, 2017
Disaggregation of Revenue [Line Items]    
Revenues $ 179,059 $ 152,396
Aerospace    
Disaggregation of Revenue [Line Items]    
Revenues 164,600 136,827
Test Systems    
Disaggregation of Revenue [Line Items]    
Revenues 14,459 15,569
Electrical Power & Motion    
Disaggregation of Revenue [Line Items]    
Revenues 72,678 72,444
Lighting & Safety    
Disaggregation of Revenue [Line Items]    
Revenues 41,642 42,670
Avionics    
Disaggregation of Revenue [Line Items]    
Revenues 33,023 9,136
Systems Certification    
Disaggregation of Revenue [Line Items]    
Revenues 4,783 2,159
Structures    
Disaggregation of Revenue [Line Items]    
Revenues 5,603 5,996
Other    
Disaggregation of Revenue [Line Items]    
Revenues $ 6,871 $ 4,422