Fair Value Measurements (Financial Assets Measured At Fair Values On Recurring Basis) (Details) (USD $)	Mar. 28, 2015	Dec. 27, 2014
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 134,753,000	$ 135,950,000
Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	4,035,000	8,729,000
Level 1 [Member] | Corporate Bonds And Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	90,114,000	88,401,000
Level 1 [Member] | United States ("US") Treasury And Government Agency Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	40,553,000	38,283,000
Level 1 [Member] | Foreign Government And Agency Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	51,000	537,000
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	34,914,000	26,173,000
Level 2 [Member] | Corporate Bonds And Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	21,607,000	17,030,000
Level 2 [Member] | United States ("US") Treasury And Government Agency Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	1,946,000	1,387,000
Level 2 [Member] | Foreign Government And Agency Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	11,130,000	7,525,000
Level 2 [Member] | US State And Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 231,000	$ 231,000