Marketable Securities Available-for-sale Securities - Continuous Loss Position (Details) - USD ($) $ in Thousands	Jul. 01, 2018	Dec. 31, 2017
Total short-term AFS securities
Short-term AFS securities
Fair value, less than 12 months	$ 217,980	$ 230,832
Gross unrealized losses, less than 12 months	(501)	(283)
Fair value, greater than 12 months	49,818	35,866
Gross unrealized losses, greater than 12 months	(243)	(157)
Fair value, total	267,798	266,698
Gross unrealized losses, total	(744)	(440)
Total long-term AFS securities
Long-term AFS securities
Fair value, less than 12 months	186,321	157,744
Gross unrealized losses, less than 12 months	(2,031)	(1,107)
Fair value, greater than 12 months	60,404	83,667
Gross unrealized losses, greater than 12 months	(875)	(998)
Fair value, total	246,725	241,411
Gross unrealized losses, total	(2,906)	(2,105)
Corporate Debt Securities
Short-term AFS securities
Fair value, less than 12 months	97,827	140,111
Gross unrealized losses, less than 12 months	(347)	(199)
Fair value, greater than 12 months	16,353	9,996
Gross unrealized losses, greater than 12 months	(106)	(28)
Fair value, total	114,180	150,107
Gross unrealized losses, total	(453)	(227)
Long-term AFS securities
Fair value, less than 12 months	112,576	81,118
Gross unrealized losses, less than 12 months	(1,094)	(579)
Fair value, greater than 12 months	1,972	10,886
Gross unrealized losses, greater than 12 months	(29)	(104)
Fair value, total	114,548	92,004
Gross unrealized losses, total	(1,123)	(683)
US Treasury Securities
Short-term AFS securities
Fair value, less than 12 months	102,834	70,951
Gross unrealized losses, less than 12 months	(142)	(34)
Fair value, greater than 12 months	0	0
Gross unrealized losses, greater than 12 months	0	0
Fair value, total	102,834	70,951
Gross unrealized losses, total	(142)	(34)
Long-term AFS securities
Fair value, less than 12 months	41,500	23,998
Gross unrealized losses, less than 12 months	(637)	(125)
Fair value, greater than 12 months	0	72,781
Gross unrealized losses, greater than 12 months	0	(894)
Fair value, total	41,500	96,779
Gross unrealized losses, total	(637)	(1,019)
U.S. governmental agency securities
Short-term AFS securities
Fair value, less than 12 months	17,319	19,770
Gross unrealized losses, less than 12 months	(12)	(50)
Fair value, greater than 12 months	33,465	25,870
Gross unrealized losses, greater than 12 months	(137)	(129)
Fair value, total	50,784	45,640
Gross unrealized losses, total	(149)	(179)
Long-term AFS securities
Fair value, less than 12 months	32,245	52,628
Gross unrealized losses, less than 12 months	(300)	(403)
Fair value, greater than 12 months	58,432	0
Gross unrealized losses, greater than 12 months	(846)	0
Fair value, total	90,677	52,628
Gross unrealized losses, total	$ (1,146)	$ (403)