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Income Taxes - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Dec. 28, 2012
Dec. 30, 2011
Income Taxes [Line Items]    
U.S. federal statutory income tax rate 35.00%  
Aggregate income tax (gain) expense $ 2.0 $ (15.1)
Deferred income tax benefit   $ 1.6
U.S. research and development tax credits, extension period (years) 2 years  
U.S. research and development tax credits, expiration date Dec. 31, 2011