Cash and Investments (Details) - USD ($) $ in Thousands	Dec. 30, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 117,162	$ 129,959
Gross Unrealized Gains	0	19
Gross Unrealized Losses	(133)	(17)
Estimated Fair Market Value	117,029	129,961
U.S. Government agency securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,500	11,412
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(5)	(7)
Estimated Fair Market Value	1,495	11,405
Commercial paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	7,952	22,402
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3)	0
Estimated Fair Market Value	7,949	22,402
Corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	48,073	14,194
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(105)	(6)
Estimated Fair Market Value	47,968	14,188
Asset-backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	10,240	5,466
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(19)	(3)
Estimated Fair Market Value	10,221	5,463
Cash [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	34,643	43,604
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	34,643	43,604
Money market funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	256	959
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	256	959
Certificates of deposits [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	14,498	23,000
Gross Unrealized Gains	0	19
Gross Unrealized Losses	(1)	0
Estimated Fair Market Value	$ 14,497	23,019
U.S. Treasury securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		5,667
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Estimated Fair Market Value		5,667
Commercial paper and corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		2,499
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Estimated Fair Market Value		2,499
Municipal securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		756
Gross Unrealized Gains		0
Gross Unrealized Losses		(1)
Estimated Fair Market Value		$ 755

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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