Marketable Securities (Maturities of Marketable Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 26, 2015
Marketable Securities [Abstract]
Amortized Cost, Due within one year	$ 6,144
Fair Value, Due within one year	6,179
Amortized Cost, Due after one year through five years	27,780
Fair Value, Due after one year through five years	27,972
Amortized Cost, Due after five years through ten years	20,317
Fair Value, Due after five years through ten years	20,162
Amortized Cost, Due after ten years	3,498
Fair Value, Due after ten years	3,498
Amortized Cost, Equity securities	1,198
Fair Value, Equity securities	9,360
Available-for-sale Securities, Amortized Cost, Total	58,937	$ 83,545
Available-for-sale Securities, Fair Value, Total	$ 67,171	$ 91,629