Cash and Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 30, 2017
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 148,863	$ 117,162
Gross Unrealized Gains	1	0
Gross Unrealized Losses	(162)	(133)
Estimated Fair Market Value	148,702	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	(1)	(5)
Estimated Fair Market Value	1,499	1,495
Commercial paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	4,974	7,952
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(3)
Estimated Fair Market Value	4,974	7,949
Corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	36,807	48,073
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(130)	(105)
Estimated Fair Market Value	36,677	47,968
Asset-backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	10,383	10,240
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(31)	(19)
Estimated Fair Market Value	10,352	10,221
Cash [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	70,657	34,643
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	70,657	34,643
Money market funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	9,563	256
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	9,563	256
Commerical paper and Certificates of deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	5,980
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Estimated Fair Market Value	5,980
Certificates of deposits [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	8,999	14,498
Gross Unrealized Gains	1	0
Gross Unrealized Losses	0	(1)
Estimated Fair Market Value	$ 9,000	$ 14,497

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

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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