Cash and Investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 28, 2015	Dec. 27, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 77,052	$ 84,012
Gross Unrealized Gains	11	3
Gross Unrealized Losses	(14)	(53)
Estimated Fair Market Value	77,049us-gaap_AvailableForSaleSecurities	83,962us-gaap_AvailableForSaleSecurities
Investment maturity period, less than	2 years	2 years
Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27,026	34,066
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	27,026	34,066
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	909	610
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	909	610
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,398	805
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	1,398	805
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,499	2,498
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(1)
Estimated Fair Market Value	2,499	2,497
U.S. Government agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	21,553	20,556
Gross Unrealized Gains	6	1
Gross Unrealized Losses	(5)	(19)
Estimated Fair Market Value	21,554	20,538
Municipal securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,020	3,755
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(2)	(7)
Estimated Fair Market Value	3,019	3,749
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,647	21,722
Gross Unrealized Gains	4	1
Gross Unrealized Losses	(7)	(26)
Estimated Fair Market Value	$ 20,644	$ 21,697

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

+ References

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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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