Cash and Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 30, 2017
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 124,113	$ 117,162
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(226)	(133)
Estimated Fair Market Value	123,887	117,029
U.S. Government agency securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,500	1,500
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(4)	(5)
Estimated Fair Market Value	1,496	1,495
Commercial paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	5,481	7,952
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(7)	(3)
Estimated Fair Market Value	5,474	7,949
Corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	37,017	48,073
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(175)	(105)
Estimated Fair Market Value	36,842	47,968
Asset-backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	7,204	10,240
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(36)	(19)
Estimated Fair Market Value	7,168	10,221
Cash [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	56,232	34,643
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	56,232	34,643
Money market funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	9,680	256
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	9,680	256
Certificates of deposits [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	6,999	14,498
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(4)	(1)
Estimated Fair Market Value	$ 6,995	$ 14,497

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
-SubTopic 10
-Section 25
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