Financial Instruments (Details 1) (USD $) In Thousands, unless otherwise specified	Dec. 29, 2012	Mar. 31, 2012
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	$ 446,942	$ 731,520
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	(3,417)	(1,617)
Available-for-Sale Securities, 12 Months or Greater, Fair Value	51,429	45,218
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	(3,767)	(3,795)
Available-for-Sale Securities, Fair Value, Total	498,371	776,738
Available-for-Sale Securities, Gross Unrealized Losses, Total	(7,184)	(5,412)
Commercial Paper [Member]
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value		79,994
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses		(1)
Available-for-Sale Securities, 12 Months or Greater, Fair Value		0
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses		0
Available-for-Sale Securities, Fair Value, Total		79,994
Available-for-Sale Securities, Gross Unrealized Losses, Total		(1)
Corporate Bonds [Member]
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	38,746	21,111
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	(148)	(184)
Available-for-Sale Securities, 12 Months or Greater, Fair Value	0	0
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	0	0
Available-for-Sale Securities, Fair Value, Total	38,746	21,111
Available-for-Sale Securities, Gross Unrealized Losses, Total	(148)	(184)
Auction Rate Securities [Member]
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	0	0
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	0	0
Available-for-Sale Securities, 12 Months or Greater, Fair Value	28,401	28,929
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	(3,499)	(3,671)
Available-for-Sale Securities, Fair Value, Total	28,401	28,929
Available-for-Sale Securities, Gross Unrealized Losses, Total	(3,499)	(3,671)
Municipal Bonds [Member]
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	6,909	2,173
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	(56)	(24)
Available-for-Sale Securities, 12 Months or Greater, Fair Value	211	366
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	(3)	(4)
Available-for-Sale Securities, Fair Value, Total	7,120	2,539
Available-for-Sale Securities, Gross Unrealized Losses, Total	(59)	(28)
U.S. Government and Agency Securities [Member]
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	99,173	460,735
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	(10)	(149)
Available-for-Sale Securities, 12 Months or Greater, Fair Value	0	0
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	0	0
Available-for-Sale Securities, Fair Value, Total	99,173	460,735
Available-for-Sale Securities, Gross Unrealized Losses, Total	(10)	(149)
Mortgage-Backed Securities [Member]
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	281,368	147,726
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	(3,099)	(1,040)
Available-for-Sale Securities, 12 Months or Greater, Fair Value	22,817	15,923
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	(265)	(120)
Available-for-Sale Securities, Fair Value, Total	304,185	163,649
Available-for-Sale Securities, Gross Unrealized Losses, Total	(3,364)	(1,160)
Debt Mutual Fund [Member]
Fair values and gross unrealized losses of the investments
Available-for-Sale Securities, Less Than 12 Months, Fair Value	20,746	19,781
Available-for-Sale Securities, Less Than 12 Months, Gross Unrealized Losses	(104)	(219)
Available-for-Sale Securities, 12 Months or Greater, Fair Value		0
Available-for-Sale Securities, 12 Months or Greater, Gross Unrealized Losses	0	0
Available-for-Sale Securities, Fair Value, Total	20,746	19,781
Available-for-Sale Securities, Gross Unrealized Losses, Total	$ (104)	$ (219)