Cash and Investments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 27, 2014	Dec. 28, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 84,012	$ 92,853
Gross Unrealized Gains	3	22
Gross Unrealized Losses	(53)	(13)
Estimated Fair Market Value	83,962us-gaap_AvailableForSaleSecurities	92,862us-gaap_AvailableForSaleSecurities
Investment maturity period, less than	2 years	2 years
Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	34,066	43,139
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	34,066	43,139
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	610	876
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	610	876
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	805	750
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	805	750
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,498	5,036
Gross Unrealized Gains		0
Gross Unrealized Losses	(1)	0
Estimated Fair Market Value	2,497	5,036
U.S. Government agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,556	11,980
Gross Unrealized Gains	1	4
Gross Unrealized Losses	(19)	(4)
Estimated Fair Market Value	20,538	11,980
Municipal securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,755	9,756
Gross Unrealized Gains	1	11
Gross Unrealized Losses	(7)	(4)
Estimated Fair Market Value	3,749	9,763
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	21,722	21,316
Gross Unrealized Gains	1	7
Gross Unrealized Losses	(26)	(5)
Estimated Fair Market Value	$ 21,697	$ 21,318

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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