Investment Securities (Available For Sale Investments) (Details) (USD $)	Dec. 27, 2014		Dec. 28, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 161,817,000		$ 128,346,000
Gross Unrealized Gains	650,000	[1]	615,000	[2]
Gross Unrealized Losses	(344,000)		(47,000)
Fair Value	162,123,000		128,914,000
Accrued interest on investments	600,000		500,000
Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,729,000		14,629,000
Fair Value	8,729,000		14,629,000
Cash Equivalents [Member] | Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,729,000		14,629,000
Fair Value	8,729,000		14,629,000
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	45,288,000		10,434,000
Gross Unrealized Gains	613,000	[1]	462,000	[2]
Gross Unrealized Losses	(16,000)		(2,000)
Fair Value	45,885,000		10,894,000
Short-Term Investments [Member] | Corporate Bonds And Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	43,777,000		7,735,000
Gross Unrealized Gains	498,000	[1]	416,000	[2]
Gross Unrealized Losses	(16,000)		(2,000)
Fair Value	44,259,000		8,149,000
Short-Term Investments [Member] | US Treasury And Government Agency Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,010,000		2,499,000
Gross Unrealized Gains	79,000	[1]	44,000	[2]
Fair Value	1,089,000		2,543,000
Short-Term Investments [Member] | Foreign Government And Agency Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	501,000
Gross Unrealized Gains	36,000	[1]
Fair Value	537,000
Short-Term Investments [Member] | US States And Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost			200,000
Gross Unrealized Gains			2,000	[2]
Fair Value			202,000
Long-Term Investment Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	107,800,000		103,283,000
Gross Unrealized Gains	37,000	[1]	153,000	[2]
Gross Unrealized Losses	(328,000)		(45,000)
Fair Value	107,509,000		103,391,000
Long-Term Investment Securities [Member] | Corporate Bonds And Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	61,357,000		74,583,000
Gross Unrealized Gains	28,000	[1]	121,000	[2]
Gross Unrealized Losses	(213,000)		(34,000)
Fair Value	61,172,000		74,670,000
Long-Term Investment Securities [Member] | US Treasury And Government Agency Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	38,650,000		26,421,000
Gross Unrealized Gains	7,000	[1]	30,000	[2]
Gross Unrealized Losses	(76,000)		(9,000)
Fair Value	38,581,000		26,442,000
Long-Term Investment Securities [Member] | Foreign Government And Agency Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,563,000		2,049,000
Gross Unrealized Gains	1,000	[1]	1,000	[2]
Gross Unrealized Losses	(39,000)		(2,000)
Fair Value	7,525,000		2,048,000
Long-Term Investment Securities [Member] | US States And Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	230,000
Gross Unrealized Gains	1,000	[1]
Fair Value	$ 231,000

[1] *        Gross unrealized gains include accrued interest on investments of $0.6 million, which are included in the Consolidated Statement of Operations. The remainder of the gross unrealized gains and losses are included the Consolidated Balance Sheet as Accumulated other comprehensive income (loss).

[2] *        Gross unrealized gains include accrued interest on investments of $0.5 million, which are included in the Consolidated Statement of Operations. The remainder of the gross unrealized gains and losses are included the Consolidated Balance Sheet as Accumulated other comprehensive income (loss).