Investments and Fair Value Measurements-AFS Investments (Details 4) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 27, 2015	Dec. 28, 2014
Fixed Income Securities [Member]
Available-for-sale investments
Amortized Cost	$ 3,196,308,000	$ 4,233,395,000
Gross Unrealized Gain	7,792,000	10,106,000
Gross Unrealized Loss	(1,518,000)	(4,740,000)
Fair Value	3,202,582,000	4,238,761,000
U.S. Treasury securities [Member]
Available-for-sale investments
Amortized Cost	7,620,000	25,194,000
Gross Unrealized Gain	20,000	0
Gross Unrealized Loss	0	(32,000)
Fair Value	7,640,000	25,162,000
U.S. Government-sponsored agency securities [Member]
Available-for-sale investments
Amortized Cost	10,213,000	7,511,000
Gross Unrealized Gain	5,000	0
Gross Unrealized Loss	(1,000)	(18,000)
Fair Value	10,217,000	7,493,000
International Government Securities [Member]
Available-for-sale investments
Amortized Cost	57,274,000	82,033,000
Gross Unrealized Gain	97,000	0
Gross Unrealized Loss	(17,000)	(314,000)
Fair Value	57,354,000	81,719,000
Corporate notes and bonds [Member]
Available-for-sale investments
Amortized Cost	555,413,000	774,869,000
Gross Unrealized Gain	502,000	325,000
Gross Unrealized Loss	(921,000)	(2,052,000)
Fair Value	554,994,000	773,142,000
Asset-backed securities [Member]
Available-for-sale investments
Amortized Cost	136,022,000	171,221,000
Gross Unrealized Gain	137,000	42,000
Gross Unrealized Loss	(89,000)	(353,000)
Fair Value	136,070,000	170,910,000
Mortgage-backed securities [Member]
Available-for-sale investments
Amortized Cost	24,260,000	48,378,000
Gross Unrealized Gain	67,000	6,000
Gross Unrealized Loss	(20,000)	(173,000)
Fair Value	24,307,000	48,211,000
Municipal notes and bonds [Member]
Available-for-sale investments
Amortized Cost	2,405,506,000	3,124,189,000
Gross Unrealized Gain	6,964,000	9,733,000
Gross Unrealized Loss	(470,000)	(1,798,000)
Fair Value	$ 2,412,000,000	$ 3,132,124,000