Summarizes Cost And Estimated Fair Value Of Short Term Fixed Income Securities (Detail) - USD ($) $ in Thousands	Sep. 28, 2018	Dec. 29, 2017
Fair Value Measurements [Line Items]
Due within one year, Amortized Cost	$ 39,966
Due between one and two years, Amortized Cost	41,871
Total Amortized Cost	81,837
Due within one year, Estimated Fair Value	39,796
Due between one and two years, Estimated Fair Value	41,577
Total Estimated Fair Value	$ 81,373	$ 71,604