Marketable Securities (Maturities of Marketable Securities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 28, 2015	Dec. 27, 2014
Marketable Securities [Abstract]
Amortized Cost, Due within one year	$ 4,527
Fair Value, Due within one year	4,567
Amortized Cost, Due after one year through five years	47,131
Fair Value, Due after one year through five years	48,344
Amortized Cost, Due after five years through ten years	19,399
Fair Value, Due after five years through ten years	19,886
Amortized Cost, Equity securities	1,198
Fair Value, Equity securities	7,683
Amortized Cost, Total	72,255	65,759
Available-for-sale Securities, Fair Value, Total	$ 80,480	$ 73,959