Marketable Securities (Schedule Of Maturities of Marketable Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 30, 2017
Marketable Securities [Abstract]
Amortized Cost, Due within one year	$ 11,738
Fair Value, Due within one year	11,761
Amortized Cost, Due after one year through five years	21,765
Fair Value, Due after one year through five years	21,910
Amortized Cost, Due after five years through ten years	19,607
Fair Value, Due after five years through ten years	19,485
Amortized Cost, Equity securities	1,198
Fair Value, Equity securities	8,053
Amortized Cost	54,308	$ 55,476
Available-for-sale Securities, Fair Value, Total	$ 61,209	$ 63,665