Investments (Maturities of Marketable Securities) (Details) - USD ($) $ in Thousands	Jun. 25, 2016	Dec. 26, 2015
Investments [Abstract]
Amortized Cost, Due within one year	$ 6,142
Fair Value, Due within one year	6,188
Amortized Cost, Due after one year through five years	44,922
Fair Value, Due after one year through five years	45,824
Amortized Cost, Due after five years through ten years	16,059
Fair Value, Due after five years through ten years	17,068
Amortized Cost, Equity securities	1,198
Fair Value, Equity securities	9,300
Available-for-sale Securities, Amortized Cost, Total	68,321	$ 83,545
Available-for-sale Securities, Fair Value, Total	$ 78,380	$ 91,629