Financial Instruments - Amortized to fair value (Details) - USD ($) $ in Thousands	Oct. 03, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	$ 373,384	$ 334,479
Marketable Securities	43,051	184,023
Amortized Cost	416,322	518,380
Gross Unrealized Gains	113	133
Gross Unrealized Losses	0	(11)
Fair Value	416,435	518,502
U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	27,312	30,375
Marketable Securities	9,025	46,989
Amortized Cost	36,320	77,316
Gross Unrealized Gains	17	48
Gross Unrealized Losses	0	0
Fair Value	36,337	77,364
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	27,955	70,103
Marketable Securities	34,026	137,034
Amortized Cost	61,885	207,063
Gross Unrealized Gains	96	85
Gross Unrealized Losses	0	(11)
Fair Value	61,981	207,137
Cash
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	128,230	126,293
Money market funds
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	$ 189,887	$ 107,708

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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