Cash and Investments (Details) - USD ($) $ in Thousands	Apr. 01, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 132,107	$ 129,959
Gross Unrealized Gains	5	19
Gross Unrealized Losses	(16)	(17)
Estimated Fair Market Value	132,096	129,961
U.S. Government agency securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	8,710	11,412
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(6)	(7)
Estimated Fair Market Value	8,704	11,405
Commercial paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	22,325	22,402
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	0
Estimated Fair Market Value	22,323	22,402
Corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	25,875	14,194
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(6)	(6)
Estimated Fair Market Value	25,869	14,188
Asset-backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	3,274	5,466
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(3)
Estimated Fair Market Value	3,273	5,463
Cash [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	45,559	43,604
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	45,559	43,604
Money market funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	858	959
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	858	959
Certificates of deposits [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	21,500	23,000
Gross Unrealized Gains	5	19
Gross Unrealized Losses	0	0
Estimated Fair Market Value	21,505	23,019
U.S. Treasury securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	3,006	5,667
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	0
Estimated Fair Market Value	3,005	5,667
Commercial paper and corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,000	2,499
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	$ 1,000	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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