Summarizes Cost And Estimated Fair Value Of Short Term Fixed Income Securities (Detail) - USD ($) $ in Thousands	Dec. 28, 2018	Dec. 29, 2017
Fair Value Measurements [Line Items]
Due within one year, Amortized Cost	$ 32,986
Due between one and two years, Amortized Cost	48,648
Total Amortized Cost	81,634
Due within one year, Estimated Fair Value	32,826
Due between one and two years, Estimated Fair Value	48,669
Total Estimated Fair Value	$ 81,495	$ 71,604