Cash and Investments (Details) - USD ($) $ in Thousands	Mar. 26, 2016	Dec. 26, 2015
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 83,354	$ 83,148
Gross Unrealized Gains	8	2
Gross Unrealized Losses	(17)	(65)
Estimated Fair Market Value	83,345	83,085
Commercial paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	699	1,884
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	699	1,884
U.S. Government agency securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	23,231	20,193
Gross Unrealized Gains	4	1
Gross Unrealized Losses	(8)	(29)
Estimated Fair Market Value	23,227	20,165
Corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	11,147	14,759
Gross Unrealized Gains	2	0
Gross Unrealized Losses	(6)	(23)
Estimated Fair Market Value	11,143	14,736
Cash [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	33,145	32,996
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	33,145	32,996
Money market funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,075	590
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	1,075	590
U.S. Treasury securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	6,971	4,411
Gross Unrealized Gains	2	0
Gross Unrealized Losses	0	(10)
Estimated Fair Market Value	6,973	4,401
Commercial paper and corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	4,452
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Estimated Fair Market Value	4,452
Commercial paper and corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		4,568
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Estimated Fair Market Value		4,568
Municipal securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,634	3,747
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(3)	(3)
Estimated Fair Market Value	$ 2,631	$ 3,745

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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