Marketable Securities (Maturities of Marketable Securities) (Details) - USD ($) $ in Thousands	Jun. 27, 2015	Dec. 27, 2014
Marketable Securities [Abstract]
Amortized Cost, Due within one year	$ 5,675
Fair Value, Due within one year	5,707
Amortized Cost, Due after one year through five years	45,173
Fair Value, Due after one year through five years	46,133
Amortized Cost, Due after five years through ten years	19,591
Fair Value, Due after five years through ten years	19,605
Amortized Cost, Equity securities	1,198
Fair Value, Equity securities	8,192
Amortized Cost, Total	71,637	$ 65,759
Available-for-sale Securities, Fair Value, Total	$ 79,637	$ 73,959