Cash and Investments (Details) - USD ($) $ in Thousands	Sep. 24, 2016	Dec. 26, 2015
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 118,497	$ 83,148
Gross Unrealized Gains	34	2
Gross Unrealized Losses	(4)	(65)
Estimated Fair Market Value	118,527	83,085
U.S. Government agency securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	14,301	20,193
Gross Unrealized Gains	11	1
Gross Unrealized Losses	0	(29)
Estimated Fair Market Value	14,312	20,165
Commercial paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	23,845	1,884
Gross Unrealized Gains	3	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	23,848	1,884
Asset-backed securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	7,470
Gross Unrealized Gains	0
Gross Unrealized Losses	(2)
Estimated Fair Market Value	7,468
Corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	11,762	14,759
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(23)
Estimated Fair Market Value	11,761	14,736
Cash [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	32,337	32,996
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	32,337	32,996
Money market funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	840	590
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	840	590
U.S. Treasury securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	6,935	4,411
Gross Unrealized Gains	9	0
Gross Unrealized Losses	0	(10)
Estimated Fair Market Value	6,944	4,401
Commercial paper and corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	4,245
Gross Unrealized Gains	0
Gross Unrealized Losses	(1)
Estimated Fair Market Value	4,244
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
Certificates of deposits [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	15,997
Gross Unrealized Gains	11
Gross Unrealized Losses	0
Estimated Fair Market Value	16,008
Municipal securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	765	3,747
Gross Unrealized Gains	0	1
Gross Unrealized Losses	0	(3)
Estimated Fair Market Value	$ 765	$ 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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