Summarizes Cost And Estimated Fair Value Of Short Term Fixed Income Securities (Detail) - USD ($) $ in Thousands	Mar. 30, 2018	Dec. 29, 2017
Fair Value Measurements [Line Items]
Due within one year, Amortized Cost	$ 47,927
Due between one and two years, Amortized Cost	28,004
Total Amortized Cost	75,931
Due within one year, Estimated Fair Value	47,725
Due between one and two years, Estimated Fair Value	27,760
Total Estimated Fair Value	$ 75,485	$ 71,604