Cash and Investments (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 26, 2015	Dec. 27, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 84,609	$ 84,012
Gross Unrealized Gains	25	3
Gross Unrealized Losses	(8)	(53)
Estimated Fair Market Value	$ 84,626	$ 83,962
Investment maturity period, less than	2 years	2 years
Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 34,485	$ 34,066
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	34,485	34,066
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	642	610
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	642	610
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,434
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Estimated Fair Market Value	6,434
Commercial paper, not included in cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,498	805
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	1,498	805
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,498
Gross Unrealized Gains		0
Gross Unrealized Losses		(1)
Estimated Fair Market Value		2,497
U.S. Government agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	21,668	20,556
Gross Unrealized Gains	17	1
Gross Unrealized Losses	(1)	(19)
Estimated Fair Market Value	21,684	20,538
Municipal securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,714	3,755
Gross Unrealized Gains	5	1
Gross Unrealized Losses	(1)	(7)
Estimated Fair Market Value	3,718	3,749
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,168	21,722
Gross Unrealized Gains	3	1
Gross Unrealized Losses	(6)	(26)
Estimated Fair Market Value	$ 16,165	$ 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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-Name Accounting Standards Codification

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