Fair Value Measurements (Narrative) (Details) - USD ($)	Sep. 26, 2015	Dec. 27, 2014
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured and recorded at fair value	$ 0
Liabilities measured and recorded at fair value	0
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments previously listed as Level 2	(10,100,000)
Assets measured and recorded at fair value	149,969,000	$ 135,950,000
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments previously listed as Level 1	(9,500,000)
Assets measured and recorded at fair value	30,818,000	26,173,000
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured and recorded at fair value	0	0
Liabilities measured and recorded at fair value	$ 0	$ 0