Summarizes Cost And Estimated Fair Value Of Short Term Fixed Income Securities (Detail) - USD ($) $ in Thousands	Jun. 29, 2018	Dec. 29, 2017
Fair Value Measurements [Line Items]
Due within one year, Amortized Cost	$ 43,947
Due between one and two years, Amortized Cost	32,008
Total Amortized Cost	75,955
Due within one year, Estimated Fair Value	43,784
Due between one and two years, Estimated Fair Value	31,750
Total Estimated Fair Value	$ 75,534	$ 71,604