Fair Value Measurements (Financial Assets Measured At Fair Values On Recurring Basis) (Details) - USD ($) $ in Thousands	Jun. 27, 2015	Dec. 27, 2014
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 140,582	$ 135,950
Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	3,465	8,729
Level 1 [Member] | Corporate Bonds And Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	92,929	88,401
Level 1 [Member] | U.S. Treasury And Government Agency Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	44,188	38,283
Level 1 [Member] | Foreign Government And Agency Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		537
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	39,934	26,173
Level 2 [Member] | Forward Currency Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	157
Level 2 [Member] | Corporate Bonds And Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	27,262	17,030
Level 2 [Member] | U.S. Treasury And Government Agency Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	1,339	1,387
Level 2 [Member] | Foreign Government And Agency Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	10,944	7,525
Level 2 [Member] | U.S. State And Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 232	$ 231