Cash and Investments (Details) - USD ($) $ in Thousands	Jul. 01, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 135,718	$ 129,959
Gross Unrealized Gains	10	19
Gross Unrealized Losses	(34)	(17)
Estimated Fair Market Value	135,694	129,961
U.S. Government agency securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,750	11,412
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(5)	(7)
Estimated Fair Market Value	2,745	11,405
Commercial paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	17,427	22,402
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3)	0
Estimated Fair Market Value	17,424	22,402
Corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	38,035	14,194
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(23)	(6)
Estimated Fair Market Value	38,012	14,188
Asset-backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	5,850	5,466
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(3)
Estimated Fair Market Value	5,849	5,463
Cash [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	33,987	43,604
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	33,987	43,604
Money market funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	5,371	959
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	5,371	959
Certificates of deposits [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	26,298	23,000
Gross Unrealized Gains	10	19
Gross Unrealized Losses	0	0
Estimated Fair Market Value	26,308	23,019
U.S. Treasury securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	3,004	5,667
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	0
Estimated Fair Market Value	3,002	5,667
Commercial paper and corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,996	2,499
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	$ 2,996	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
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