Cash, Cash Equivalents, and Investments - Gross Unrealized Losses and Fair Values for Available-for-Sale Investments (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 27, 2020	Sep. 29, 2019	Sep. 27, 2020	Sep. 29, 2019
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	$ 53,601,000		$ 53,601,000
Unrealized losses, less than 12 months	(152,000)		(152,000)
Fair value, 12 months or greater	0		0
Unrealized losses, 12 months or greater	0		0
Total fair value	53,601,000		53,601,000
Total Unrealized Losses	(152,000)		(152,000)
Gross credit losses recorded	0	$ 0	160,000	$ 0
Gross recoveries	0	$ 0	85,000	$ 0
Treasury Bills
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	11,543,000		11,543,000
Unrealized losses, less than 12 months	(10,000)		(10,000)
Fair value, 12 months or greater	0		0
Unrealized losses, 12 months or greater	0		0
Total fair value	11,543,000		11,543,000
Total Unrealized Losses	(10,000)		(10,000)
Corporate Bonds
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	42,058,000		42,058,000
Unrealized losses, less than 12 months	(142,000)		(142,000)
Fair value, 12 months or greater	0		0
Unrealized losses, 12 months or greater	0		0
Total fair value	42,058,000		42,058,000
Total Unrealized Losses	$ (142,000)		$ (142,000)