Marketable Securities - Available-for-sale Securities - Continuous Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 30, 2018
Total short-term AFS securities
Short-term AFS securities
Fair value, less than 12 months	$ 25,652	$ 160,979
Gross unrealized losses, less than 12 months	(18)	(150)
Fair value, greater than 12 months	162,248	169,977
Gross unrealized losses, greater than 12 months	(329)	(1,200)
Fair value, total	187,900	330,956
Gross unrealized losses, total	(347)	(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	36,827	123,713
Gross unrealized losses, less than 12 months	(74)	(635)
Fair value, greater than 12 months	17,854	62,895
Gross unrealized losses, greater than 12 months	(20)	(912)
Fair value, total	54,681	186,608
Gross unrealized losses, total	(94)	(1,547)
US Treasury Securities
Short-term AFS securities
Fair value, less than 12 months	8,750	70,830
Gross unrealized losses, less than 12 months	(2)	(31)
Fair value, greater than 12 months	37,911	28,207
Gross unrealized losses, greater than 12 months	(109)	(201)
Fair value, total	46,661	99,037
Gross unrealized losses, total	(111)	(232)
Long-term AFS securities
Fair value, less than 12 months	10,988	21,579
Gross unrealized losses, less than 12 months	(20)	(36)
Fair value, greater than 12 months	1,101	11,868
Gross unrealized losses, greater than 12 months	(2)	(132)
Fair value, total	12,089	33,447
Gross unrealized losses, total	(22)	(168)
Corporate Debt Securities
Short-term AFS securities
Fair value, less than 12 months	7,159	76,886
Gross unrealized losses, less than 12 months	(2)	(115)
Fair value, greater than 12 months	46,538	61,459
Gross unrealized losses, greater than 12 months	(114)	(349)
Fair value, total	53,697	138,345
Gross unrealized losses, total	(116)	(464)
Long-term AFS securities
Fair value, less than 12 months	25,839	81,655
Gross unrealized losses, less than 12 months	(54)	(570)
Fair value, greater than 12 months	10,761	27,265
Gross unrealized losses, greater than 12 months	(10)	(462)
Fair value, total	36,600	108,920
Gross unrealized losses, total	(64)	(1,032)
U.S. governmental agency securities
Short-term AFS securities
Fair value, less than 12 months	9,743	11,664
Gross unrealized losses, less than 12 months	(14)	(4)
Fair value, greater than 12 months	77,799	80,311
Gross unrealized losses, greater than 12 months	(106)	(650)
Fair value, total	87,542	91,975
Gross unrealized losses, total	(120)	(654)
Long-term AFS securities
Fair value, less than 12 months	0	20,479
Gross unrealized losses, less than 12 months	0	(29)
Fair value, greater than 12 months	5,992	23,762
Gross unrealized losses, greater than 12 months	(8)	(318)
Fair value, total	5,992	44,241
Gross unrealized losses, total	$ (8)	$ (347)