Summarizes Cost And Estimated Fair Value Of Short Term Fixed Income Securities (Detail) - USD ($) $ in Thousands	Sep. 29, 2017	Dec. 30, 2016
Fair Value Measurements [Line Items]
Due within one year, Amortized Cost	$ 40,000
Due between one and two years, Amortized Cost	35,997
Total Amortized Cost	75,997
Due within one year, Estimated Fair Value	39,919
Due between one and two years, Estimated Fair Value	35,863
Total Estimated Fair Value	$ 75,782	$ 58,755