Financial Instruments - Amortized to fair value (Details) - USD ($) $ in Thousands	Jul. 04, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	$ 343,476	$ 334,479
Marketable Securities	104,755	184,023
Amortized Cost	447,946	518,380
Gross Unrealized Gains	287	133
Gross Unrealized Losses	(2)	(11)
Fair Value	448,231	518,502
U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	0	30,375
Marketable Securities	24,083	46,989
Amortized Cost	24,016	77,316
Gross Unrealized Gains	67	48
Gross Unrealized Losses	0	0
Fair Value	24,083	77,364
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	0	70,103
Marketable Securities	80,672	137,034
Amortized Cost	80,454	207,063
Gross Unrealized Gains	220	85
Gross Unrealized Losses	(2)	(11)
Fair Value	80,672	207,137
Cash
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	102,227	126,293
Money market funds
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	$ 241,249	$ 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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