Marketable Securities Available-for-sale Securities - Continuous Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 30, 2018
Total short-term AFS securities
Short-term AFS securities
Fair value, less than 12 months	$ 90,506	$ 160,979
Gross unrealized losses, less than 12 months	(21)	(150)
Fair value, greater than 12 months	173,492	169,977
Gross unrealized losses, greater than 12 months	(787)	(1,200)
Fair value, total	263,998	330,956
Gross unrealized losses, total	(808)	(1,350)
Certificates of deposit
Short-term AFS securities
Fair value, less than 12 months		1,599
Gross unrealized losses, less than 12 months		0
Fair value, greater than 12 months		0
Gross unrealized losses, greater than 12 months		0
Fair value, total		1,599
Gross unrealized losses, total		0
Total long-term AFS securities
Long-term AFS securities
Fair value, less than 12 months	51,438	123,713
Gross unrealized losses, less than 12 months	(99)	(635)
Fair value, greater than 12 months	43,281	62,895
Gross unrealized losses, greater than 12 months	(313)	(912)
Fair value, total	94,719	186,608
Gross unrealized losses, total	(412)	(1,547)
Corporate Debt Securities
Short-term AFS securities
Fair value, less than 12 months	41,565	76,886
Gross unrealized losses, less than 12 months	(8)	(115)
Fair value, greater than 12 months	65,613	61,459
Gross unrealized losses, greater than 12 months	(271)	(349)
Fair value, total	107,178	138,345
Gross unrealized losses, total	(279)	(464)
Long-term AFS securities
Fair value, less than 12 months	28,658	81,655
Gross unrealized losses, less than 12 months	(57)	(570)
Fair value, greater than 12 months	15,799	27,265
Gross unrealized losses, greater than 12 months	(108)	(462)
Fair value, total	44,457	108,920
Gross unrealized losses, total	(165)	(1,032)
US Treasury Securities
Short-term AFS securities
Fair value, less than 12 months	40,594	70,830
Gross unrealized losses, less than 12 months	(7)	(31)
Fair value, greater than 12 months	36,612	28,207
Gross unrealized losses, greater than 12 months	(176)	(201)
Fair value, total	77,206	99,037
Gross unrealized losses, total	(183)	(232)
Long-term AFS securities
Fair value, less than 12 months	9,491	21,579
Gross unrealized losses, less than 12 months	(20)	(36)
Fair value, greater than 12 months	15,553	11,868
Gross unrealized losses, greater than 12 months	(135)	(132)
Fair value, total	25,044	33,447
Gross unrealized losses, total	(155)	(168)
U.S. governmental agency securities
Short-term AFS securities
Fair value, less than 12 months	8,347	11,664
Gross unrealized losses, less than 12 months	(6)	(4)
Fair value, greater than 12 months	71,267	80,311
Gross unrealized losses, greater than 12 months	(340)	(650)
Fair value, total	79,614	91,975
Gross unrealized losses, total	(346)	(654)
Long-term AFS securities
Fair value, less than 12 months	13,289	20,479
Gross unrealized losses, less than 12 months	(22)	(29)
Fair value, greater than 12 months	11,929	23,762
Gross unrealized losses, greater than 12 months	(70)	(318)
Fair value, total	25,218	44,241
Gross unrealized losses, total	$ (92)	$ (347)