Summarizes Cost And Estimated Fair Value Of Short Term Fixed Income Securities (Detail) - USD ($) $ in Thousands	Mar. 29, 2019	Dec. 28, 2018
Fair Value Measurements [Line Items]
Due within one year, Amortized Cost	$ 46,919
Due between one and two years, Amortized Cost	45,694
Total Amortized Cost	92,613
Due within one year, Estimated Fair Value	46,815
Due between one and two years, Estimated Fair Value	45,865
Total Estimated Fair Value	$ 92,680	$ 81,495