Marketable Securities - Available for Sale (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 27, 2020	Dec. 29, 2019
Debt Securities, Available-for-sale [Line Items]
Net unrealized loss in other comprehensive income	$ 4,700	$ 800
Short-term AFS securities
Amortized cost, short-term AFS securities	308,036	201,495
Gross unrealized gains, short-term AFS securities	723	314
Gross unrealized losses, short-term AFS securities	(25)	(24)
Fair value, short-term AFS securities	308,734	201,785
Long-term AFS securities
Amortized cost, long-term AFS securities	271,630	251,206
Gross unrealized gains, long-term AFS securities	4,145	706
Gross unrealized losses, long-term AFS securities	(126)	(216)
Fair value, long-term AFS securities	275,649	251,696
Corporate debt securities
Short-term AFS securities
Amortized cost, short-term AFS securities	119,042	98,864
Gross unrealized gains, short-term AFS securities	561	271
Gross unrealized losses, short-term AFS securities	(17)	(9)
Fair value, short-term AFS securities	119,586	99,126
Long-term AFS securities
Amortized cost, long-term AFS securities	118,690	103,149
Gross unrealized gains, long-term AFS securities	1,713	617
Gross unrealized losses, long-term AFS securities	(22)	(29)
Fair value, long-term AFS securities	120,381	103,737
U.S. Treasury securities
Short-term AFS securities
Amortized cost, short-term AFS securities	97,712	43,098
Gross unrealized gains, short-term AFS securities	94	8
Gross unrealized losses, short-term AFS securities	(4)	(11)
Fair value, short-term AFS securities	97,802	43,095
Long-term AFS securities
Amortized cost, long-term AFS securities	88,059	101,457
Gross unrealized gains, long-term AFS securities	2,343	84
Gross unrealized losses, long-term AFS securities	0	(103)
Fair value, long-term AFS securities	90,402	101,438
U.S. governmental agency securities
Short-term AFS securities
Amortized cost, short-term AFS securities	47,759	37,471
Gross unrealized gains, short-term AFS securities	68	35
Gross unrealized losses, short-term AFS securities	(4)	(4)
Fair value, short-term AFS securities	47,823	37,502
Long-term AFS securities
Amortized cost, long-term AFS securities	64,881	46,600
Gross unrealized gains, long-term AFS securities	89	5
Gross unrealized losses, long-term AFS securities	(104)	(84)
Fair value, long-term AFS securities	64,866	46,521
Commercial paper
Short-term AFS securities
Amortized cost, short-term AFS securities	43,523	12,561
Gross unrealized gains, short-term AFS securities	0	0
Gross unrealized losses, short-term AFS securities	0	0
Fair value, short-term AFS securities	$ 43,523	12,561
Certificates of deposit
Short-term AFS securities
Amortized cost, short-term AFS securities		9,501
Gross unrealized gains, short-term AFS securities		0
Gross unrealized losses, short-term AFS securities		0
Fair value, short-term AFS securities		$ 9,501