Investments and Fair Value Measurements-AFS Investments (Details 4) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 28, 2015	Dec. 28, 2014
Fixed Income Securities [Member]
Available-for-sale investments
Amortized Cost	$ 3,337,936,000	$ 4,233,395,000
Gross Unrealized Gain	5,529,000	10,106,000
Gross Unrealized Loss	(3,637,000)	(4,740,000)
Fair Value	3,339,828,000	4,238,761,000
U.S. Treasury securities [Member]
Available-for-sale investments
Amortized Cost	5,440,000	25,194,000
Gross Unrealized Gain	8,000	0
Gross Unrealized Loss	(21,000)	(32,000)
Fair Value	5,427,000	25,162,000
U.S. Government-sponsored agency securities [Member]
Available-for-sale investments
Amortized Cost	7,336,000	7,511,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(54,000)	(18,000)
Fair Value	7,282,000	7,493,000
International Government Securities [Member]
Available-for-sale investments
Amortized Cost	57,288,000	82,033,000
Gross Unrealized Gain	44,000	0
Gross Unrealized Loss	(59,000)	(314,000)
Fair Value	57,273,000	81,719,000
Corporate notes and bonds [Member]
Available-for-sale investments
Amortized Cost	587,630,000	774,869,000
Gross Unrealized Gain	484,000	325,000
Gross Unrealized Loss	(1,004,000)	(2,052,000)
Fair Value	587,110,000	773,142,000
Asset-backed securities [Member]
Available-for-sale investments
Amortized Cost	132,786,000	171,221,000
Gross Unrealized Gain	71,000	42,000
Gross Unrealized Loss	(97,000)	(353,000)
Fair Value	132,760,000	170,910,000
Mortgage-backed securities [Member]
Available-for-sale investments
Amortized Cost	26,138,000	48,378,000
Gross Unrealized Gain	47,000	6,000
Gross Unrealized Loss	(36,000)	(173,000)
Fair Value	26,149,000	48,211,000
Municipal notes and bonds [Member]
Available-for-sale investments
Amortized Cost	2,521,318,000	3,124,189,000
Gross Unrealized Gain	4,875,000	9,733,000
Gross Unrealized Loss	(2,366,000)	(1,798,000)
Fair Value	$ 2,523,827,000	$ 3,132,124,000