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Pension and Other Employee Benefits - Additional Information (Detail) - USD ($)
$ in Millions
Sep. 30, 2017
Sep. 24, 2016
Other Liabilities Disclosure [Abstract]    
Defined benefit pension plan, liabilities $ (9.9) $ (11.0)
Projected benefit obligations in excess of plan assets (9.9) (11.0)
Accumulated benefit obligation (9.9) (11.0)
Projected benefit obligation for long-term service awards $ 0.1 $ 0.1