Investment Securities (Available For Sale Investments) (Details) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 27, 2015	Dec. 27, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 179,769	$ 161,817
Gross Unrealized Gains	[1]	770	650
Gross Unrealized Losses		(180)	(344)
Fair Value		180,359	162,123
Accrued interest on investments		600	600
Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		3,465	8,729
Fair Value		3,465	8,729
Cash Equivalents [Member] | Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		3,465	8,729
Fair Value		3,465	8,729
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		44,737	45,288
Gross Unrealized Gains	[1]	658	613
Gross Unrealized Losses		(9)	(16)
Fair Value		45,386	45,885
Short-Term Investments [Member] | Corporate Bonds And Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		39,970	43,777
Gross Unrealized Gains	[1]	507	498
Gross Unrealized Losses		(6)	(16)
Fair Value		40,471	44,259
Short-Term Investments [Member] | U.S. Treasury And Government Agency Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		3,028	1,010
Gross Unrealized Gains	[1]	106	79
Fair Value		3,134	1,089
Short-Term Investments [Member] | Foreign Government And Agency Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,509	501
Gross Unrealized Gains	[1]	43	36
Gross Unrealized Losses		(3)
Fair Value		1,549	537
Short-Term Investments [Member] | US States And Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		230
Gross Unrealized Gains	[1]	2
Fair Value		232
Long-Term Investment Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		131,567	107,800
Gross Unrealized Gains	[1]	112	37
Gross Unrealized Losses		(171)	(328)
Fair Value		131,508	107,509
Long-Term Investment Securities [Member] | Corporate Bonds And Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		79,801	61,357
Gross Unrealized Gains	[1]	51	28
Gross Unrealized Losses		(132)	(213)
Fair Value		79,720	61,172
Long-Term Investment Securities [Member] | U.S. Treasury And Government Agency Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		42,356	38,650
Gross Unrealized Gains	[1]	59	7
Gross Unrealized Losses		(22)	(76)
Fair Value		42,393	38,581
Long-Term Investment Securities [Member] | Foreign Government And Agency Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		9,410	7,563
Gross Unrealized Gains	[1]	2	1
Gross Unrealized Losses		(17)	(39)
Fair Value		$ 9,395	7,525
Long-Term Investment Securities [Member] | US States And Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost			230
Gross Unrealized Gains	[1]		1
Fair Value			$ 231

[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 in the Consolidated Balance Sheet as Accumulated other comprehensive income (loss).