Marketable Securities Available-for-sale Securities - Continuous Loss Position (Details)	9 Months Ended
	Sep. 24, 2017 USD ($)
Long-term AFS securities
Other-than-temporary impairment loss	$ 0
Total short-term AFS securities
Short-term AFS securities
Fair value, less than 12 months	217,313,000
Gross unrealized losses, less than 12 months	(175,000)
Fair value, 12 months or greater	11,464,000
Gross unrealized losses, 12 months or greater	(38,000)
Fair value, total	228,777,000
Gross unrealized losses, total	(213,000)
Total long-term AFS securities
Long-term AFS securities
Fair value, less than 12 months	167,190,000
Gross unrealized losses, less than 12 months	(560,000)
Fair value, 12 months or greater	48,615,000
Gross unrealized losses, 12 months or greater	(367,000)
Fair value, total	215,805,000
Gross unrealized losses, total	(927,000)
US Treasury Securities
Short-term AFS securities
Fair value, less than 12 months	73,175,000
Gross unrealized losses, less than 12 months	(45,000)
Fair value, 12 months or greater	0
Gross unrealized losses, 12 months or greater	0
Fair value, total	73,175,000
Gross unrealized losses, total	(45,000)
Long-term AFS securities
Fair value, less than 12 months	53,142,000
Gross unrealized losses, less than 12 months	(52,000)
Fair value, 12 months or greater	39,697,000
Gross unrealized losses, 12 months or greater	0
Fair value, total	92,839,000
Gross unrealized losses, total	(52,000)
Corporate Debt Securities
Short-term AFS securities
Fair value, less than 12 months	101,648,000
Gross unrealized losses, less than 12 months	(77,000)
Fair value, 12 months or greater	2,500,000
Gross unrealized losses, 12 months or greater	(2,000)
Fair value, total	104,148,000
Gross unrealized losses, total	(79,000)
Long-term AFS securities
Fair value, less than 12 months	66,428,000
Gross unrealized losses, less than 12 months	(196,000)
Fair value, 12 months or greater	8,918,000
Gross unrealized losses, 12 months or greater	(63,000)
Fair value, total	75,346,000
Gross unrealized losses, total	(259,000)
US Government Agencies Debt Securities
Short-term AFS securities
Fair value, less than 12 months	42,490,000
Gross unrealized losses, less than 12 months	(53,000)
Fair value, 12 months or greater	8,964,000
Gross unrealized losses, 12 months or greater	(36,000)
Fair value, total	51,454,000
Gross unrealized losses, total	(89,000)
Long-term AFS securities
Fair value, less than 12 months	47,620,000
Gross unrealized losses, less than 12 months	(312,000)
Fair value, 12 months or greater	0
Gross unrealized losses, 12 months or greater	(304,000)
Fair value, total	47,620,000
Gross unrealized losses, total	$ (616,000)