Marketable Securities - Available for Sale (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 29, 2020	Dec. 29, 2019
Debt Securities, Available-for-sale [Line Items]
Net unrealized gains (loss) in other comprehensive income	$ 1,500,000	$ 800,000
OTTI loss recognized	0
Short-term AFS securities
Amortized cost, short-term AFS securities	216,678,000	201,495,000
Gross unrealized gains, short-term AFS	553,000	314,000
Gross unrealized losses, short-term AFS	(573,000)	(24,000)
Fair value, short-term AFS securities	216,658,000	201,785,000
Long-term AFS securities
Amortized cost, long-term AFS securities	250,410,000	251,206,000
Gross unrealized gains, long-term AFS	3,259,000	706,000
Gross unrealized losses, long-term AFS	(1,743,000)	(216,000)
Fair value, long-term AFS securities	251,926,000	251,696,000
Corporate debt securities
Short-term AFS securities
Amortized cost, short-term AFS securities	90,893,000	98,864,000
Gross unrealized gains, short-term AFS	23,000	271,000
Gross unrealized losses, short-term AFS	(570,000)	(9,000)
Fair value, short-term AFS securities	90,346,000	99,126,000
Long-term AFS securities
Amortized cost, long-term AFS securities	99,044,000	103,149,000
Gross unrealized gains, long-term AFS	141,000	617,000
Gross unrealized losses, long-term AFS	(1,740,000)	(29,000)
Fair value, long-term AFS securities	97,445,000	103,737,000
U.S. Treasury securities
Short-term AFS securities
Amortized cost, short-term AFS securities	66,792,000	43,098,000
Gross unrealized gains, short-term AFS	393,000	8,000
Gross unrealized losses, short-term AFS	(2,000)	(11,000)
Fair value, short-term AFS securities	67,183,000	43,095,000
Long-term AFS securities
Amortized cost, long-term AFS securities	92,720,000	101,457,000
Gross unrealized gains, long-term AFS	2,857,000	84,000
Gross unrealized losses, long-term AFS	0	(103,000)
Fair value, long-term AFS securities	95,577,000	101,438,000
U.S. governmental agency securities
Short-term AFS securities
Amortized cost, short-term AFS securities	29,613,000	37,471,000
Gross unrealized gains, short-term AFS	137,000	35,000
Gross unrealized losses, short-term AFS	(1,000)	(4,000)
Fair value, short-term AFS securities	29,749,000	37,502,000
Long-term AFS securities
Amortized cost, long-term AFS securities	58,646,000	46,600,000
Gross unrealized gains, long-term AFS	261,000	5,000
Gross unrealized losses, long-term AFS	(3,000)	(84,000)
Fair value, long-term AFS securities	58,904,000	46,521,000
Certificates of deposit
Short-term AFS securities
Amortized cost, short-term AFS securities	10,601,000	9,501,000
Gross unrealized gains, short-term AFS	0	0
Gross unrealized losses, short-term AFS	0	0
Fair value, short-term AFS securities	10,601,000	9,501,000
Commercial paper
Short-term AFS securities
Amortized cost, short-term AFS securities	18,779,000	12,561,000
Gross unrealized gains, short-term AFS	0	0
Gross unrealized losses, short-term AFS	0	0
Fair value, short-term AFS securities	$ 18,779,000	$ 12,561,000