Cash and Investments (Details) - USD ($) $ in Thousands	Sep. 29, 2018	Dec. 30, 2017
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 173,046	$ 117,162
Gross Unrealized Gains	6	0
Gross Unrealized Losses	(114)	(133)
Estimated Fair Market Value	172,938	117,029
Cash [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	94,419	34,643
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	94,419	34,643
Money market funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,684	256
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	1,684	256
Certificates of deposits [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	14,496	14,498
Gross Unrealized Gains	6	0
Gross Unrealized Losses	0	(1)
Estimated Fair Market Value	14,502	14,497
U.S. Government agency securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		1,500
Gross Unrealized Gains		0
Gross Unrealized Losses		(5)
Estimated Fair Market Value		1,495
Commercial paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	11,185	7,952
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(3)
Estimated Fair Market Value	11,185	7,949
Corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	37,038	48,073
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(88)	(105)
Estimated Fair Market Value	36,950	47,968
Asset-backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	14,224	10,240
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(26)	(19)
Estimated Fair Market Value	$ 14,198	$ 10,221

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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