Cash and Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 26, 2015
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 129,959	$ 83,148
Gross Unrealized Gains	19	2
Gross Unrealized Losses	(17)	(65)
Estimated Fair Market Value	129,961	83,085
Commercial paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	22,402	1,884
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	22,402	1,884
U.S. Government agency securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	11,412	20,193
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(7)	(29)
Estimated Fair Market Value	11,405	20,165
Corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	14,194	14,759
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(6)	(23)
Estimated Fair Market Value	14,188	14,736
Asset-backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	5,466
Gross Unrealized Gains	0
Gross Unrealized Losses	(3)
Estimated Fair Market Value	5,463
Cash [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	43,604	32,996
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	43,604	32,996
Money market funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	959	590
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	959	590
U.S. Treasury securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	5,667	4,411
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(10)
Estimated Fair Market Value	5,667	4,401
Certificates of deposits [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	23,000
Gross Unrealized Gains	19
Gross Unrealized Losses	0
Estimated Fair Market Value	23,019
Commercial paper and corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,499	4,568
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	2,499	4,568
Municipal securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	756	3,747
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(1)	(3)
Estimated Fair Market Value	$ 755	$ 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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