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Description of business and summary of significant accounting policies - Additional Information (Detail)
$ in Millions
3 Months Ended 9 Months Ended 12 Months Ended
Oct. 01, 2017
USD ($)
Jul. 02, 2017
USD ($)
Apr. 02, 2017
USD ($)
Jan. 01, 2017
USD ($)
Oct. 02, 2016
USD ($)
Jul. 03, 2016
USD ($)
Apr. 03, 2016
USD ($)
Jan. 03, 2016
USD ($)
Jul. 02, 2017
segment
Oct. 01, 2017
USD ($)
segment
shares
Oct. 02, 2016
USD ($)
Sep. 27, 2015
USD ($)
shares
Basis of Presentation [Line Items]                        
Number of Reportable Segments | segment                 1 1    
Stock awards excluded from computation of diluted EPS | shares                   0   200,000
Net income | $ $ 102.0 $ 13.6 $ 41.2 $ 19.5 $ 40.5 $ 115.2 $ (212.0) $ 23.7   $ 176.3 $ (32.6) $ 84.6
International                        
Basis of Presentation [Line Items]                        
Percentage of net sales from international market                   67.00% 62.00% 51.00%
Defense And Security                        
Basis of Presentation [Line Items]                        
Concentration of credit risk in major customer                   26.00%    
Internal Revenue Service (IRS) | Minimum                        
Basis of Presentation [Line Items]                        
Open tax years by major tax jurisdiction                   2007    
Internal Revenue Service (IRS) | Maximum                        
Basis of Presentation [Line Items]                        
Open tax years by major tax jurisdiction                   2016    
Restricted Stock Award                        
Basis of Presentation [Line Items]                        
Award vesting period                 3 years 3 years