Marketable Securities - Available for Sale (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 28, 2020	Dec. 29, 2019
Debt Securities, Available-for-sale [Line Items]
Net unrealized gains (loss) in other comprehensive income	$ 5,600	$ 800
Short-term AFS securities
Amortized cost, short-term AFS securities	239,387	201,495
Gross unrealized gains, short-term AFS	1,028	314
Gross unrealized losses, short-term AFS	(15)	(24)
Fair value, short-term AFS securities	240,400	201,785
Long-term AFS securities
Amortized cost, long-term AFS securities	262,387	251,206
Gross unrealized gains, long-term AFS	4,590	706
Gross unrealized losses, long-term AFS	(31)	(216)
Fair value, long-term AFS securities	266,946	251,696
Corporate debt securities
Short-term AFS securities
Amortized cost, short-term AFS securities	105,615	98,864
Gross unrealized gains, short-term AFS	669	271
Gross unrealized losses, short-term AFS	(13)	(9)
Fair value, short-term AFS securities	106,271	99,126
Long-term AFS securities
Amortized cost, long-term AFS securities	114,618	103,149
Gross unrealized gains, long-term AFS	1,751	617
Gross unrealized losses, long-term AFS	(28)	(29)
Fair value, long-term AFS securities	116,341	103,737
U.S. Treasury securities
Short-term AFS securities
Amortized cost, short-term AFS securities	78,826	43,098
Gross unrealized gains, short-term AFS	179	8
Gross unrealized losses, short-term AFS	(1)	(11)
Fair value, short-term AFS securities	79,004	43,095
Long-term AFS securities
Amortized cost, long-term AFS securities	92,680	101,457
Gross unrealized gains, long-term AFS	2,714	84
Gross unrealized losses, long-term AFS	0	(103)
Fair value, long-term AFS securities	95,394	101,438
U.S. governmental agency securities
Short-term AFS securities
Amortized cost, short-term AFS securities	35,965	37,471
Gross unrealized gains, short-term AFS	180	35
Gross unrealized losses, short-term AFS	(1)	(4)
Fair value, short-term AFS securities	36,144	37,502
Long-term AFS securities
Amortized cost, long-term AFS securities	55,089	46,600
Gross unrealized gains, long-term AFS	125	5
Gross unrealized losses, long-term AFS	(3)	(84)
Fair value, long-term AFS securities	55,211	46,521
Commercial paper
Short-term AFS securities
Amortized cost, short-term AFS securities	15,981	12,561
Gross unrealized gains, short-term AFS	0	0
Gross unrealized losses, short-term AFS	0	0
Fair value, short-term AFS securities	15,981	12,561
Certificates of deposit
Short-term AFS securities
Amortized cost, short-term AFS securities	3,000	9,501
Gross unrealized gains, short-term AFS	0	0
Gross unrealized losses, short-term AFS	0	0
Fair value, short-term AFS securities	$ 3,000	$ 9,501