Investments (Maturities of Marketable Securities) (Details) - USD ($) $ in Thousands	Mar. 26, 2016	Dec. 26, 2015
Investments [Abstract]
Amortized Cost, Due within one year	$ 5,401
Fair Value, Due within one year	5,439
Amortized Cost, Due after one year through five years	46,389
Fair Value, Due after one year through five years	47,209
Amortized Cost, Due after five years through ten years	16,372
Fair Value, Due after five years through ten years	17,056
Amortized Cost, Equity securities	1,198
Fair Value, Equity securities	8,857
Available-for-sale Securities, Amortized Cost, Total	69,360	$ 83,545
Available-for-sale Securities, Fair Value, Total	$ 78,561	$ 91,629