Cash, Cash Equivalents, and Investments - Gross Unrealized Losses and Fair Values for Available-for-Sale Investments (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 28, 2020	Jun. 30, 2019	Jun. 28, 2020	Jun. 30, 2019
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	$ 72,657,000		$ 72,657,000
Unrealized losses, less than 12 months	(372,000)		(372,000)
Fair value, 12 months or greater	4,225,000		4,225,000
Unrealized losses, 12 months or greater	(26,000)		(26,000)
Total fair value	76,882,000		76,882,000
Total unrealized losses	398,000		398,000
Gross credit losses recorded	0	$ 0	160,000	$ 0
Gross recoveries	85,000	$ 0	85,000	$ 0
Treasury Bills
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	12,962,000		12,962,000
Unrealized losses, less than 12 months	(1,000)		(1,000)
Fair value, 12 months or greater	0		0
Unrealized losses, 12 months or greater	0		0
Total fair value	12,962,000		12,962,000
Total unrealized losses	1,000		1,000
Agency Bonds
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	3,128,000		3,128,000
Unrealized losses, less than 12 months	(2,000)		(2,000)
Fair value, 12 months or greater	2,784,000		2,784,000
Unrealized losses, 12 months or greater	(16,000)		(16,000)
Total fair value	5,912,000		5,912,000
Total unrealized losses	18,000		18,000
Corporate Bonds
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	49,525,000		49,525,000
Unrealized losses, less than 12 months	(363,000)		(363,000)
Fair value, 12 months or greater	1,181,000		1,181,000
Unrealized losses, 12 months or greater	(9,000)		(9,000)
Total fair value	50,706,000		50,706,000
Total unrealized losses	372,000		372,000
Asset-Backed Securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	5,749,000		5,749,000
Unrealized losses, less than 12 months	(1,000)		(1,000)
Fair value, 12 months or greater	260,000		260,000
Unrealized losses, 12 months or greater	(1,000)		(1,000)
Total fair value	6,009,000		6,009,000
Total unrealized losses	2,000		2,000
Municipal Bonds
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	1,293,000		1,293,000
Unrealized losses, less than 12 months	(5,000)		(5,000)
Fair value, 12 months or greater	0		0
Unrealized losses, 12 months or greater	0		0
Total fair value	1,293,000		1,293,000
Total unrealized losses	$ 5,000		$ 5,000