Balance Sheet Accounts (Schedule Of Marketable Securities In An Unrealized Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2012
Marketable Securities And Unrealized Loss Position [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	$ 240,085
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(1,815)
Marketable securities in an unrealized loss position for 12 months or greater, Fair Value	26,416
Marketable securities in an unrealized loss position for 12 months or greater, Unrealized Losses	(392)
Marketable securities in an unrealized loss position, Fair Value	266,501
Marketable securities in an unrealized loss position, Unrealized Losses	(2,207)
Minimum [Member]
Marketable Securities And Unrealized Loss Position [Line Items]
Unrealized losses on fixed rate investments, lower range value	1,000
Maximum [Member]
Marketable Securities And Unrealized Loss Position [Line Items]
Unrealized losses on fixed rate investments, upper range value	163,000
Corporate Notes And Obligations [Member]
Marketable Securities And Unrealized Loss Position [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	163,711
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(1,545)
Marketable securities in an unrealized loss position for 12 months or greater, Fair Value	7,364
Marketable securities in an unrealized loss position for 12 months or greater, Unrealized Losses	(62)
Marketable securities in an unrealized loss position, Fair Value	171,075
Marketable securities in an unrealized loss position, Unrealized Losses	(1,607)
U.S. Treasury Securities [Member]
Marketable Securities And Unrealized Loss Position [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	39,037
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(2)
Marketable securities in an unrealized loss position for 12 months or greater, Fair Value	0
Marketable securities in an unrealized loss position for 12 months or greater, Unrealized Losses	0
Marketable securities in an unrealized loss position, Fair Value	39,037
Marketable securities in an unrealized loss position, Unrealized Losses	(2)
Mortgage Backed Securities [Member]
Marketable Securities And Unrealized Loss Position [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	1,339
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(73)
Marketable securities in an unrealized loss position for 12 months or greater, Fair Value	4,252
Marketable securities in an unrealized loss position for 12 months or greater, Unrealized Losses	(82)
Marketable securities in an unrealized loss position, Fair Value	5,591
Marketable securities in an unrealized loss position, Unrealized Losses	(155)
Municipal Securities [Member]
Marketable Securities And Unrealized Loss Position [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	0
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	0
Marketable securities in an unrealized loss position for 12 months or greater, Fair Value	1,690
Marketable securities in an unrealized loss position for 12 months or greater, Unrealized Losses	(11)
Marketable securities in an unrealized loss position, Fair Value	1,690
Marketable securities in an unrealized loss position, Unrealized Losses	(11)
Collateralized Mortgage Obligations [Member]
Marketable Securities And Unrealized Loss Position [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	23,614
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(189)
Marketable securities in an unrealized loss position for 12 months or greater, Fair Value	13,110
Marketable securities in an unrealized loss position for 12 months or greater, Unrealized Losses	(237)
Marketable securities in an unrealized loss position, Fair Value	36,724
Marketable securities in an unrealized loss position, Unrealized Losses	(426)
U.S. Agency Obligations [Member]
Marketable Securities And Unrealized Loss Position [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	12,384
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(6)
Marketable securities in an unrealized loss position for 12 months or greater, Fair Value	0
Marketable securities in an unrealized loss position for 12 months or greater, Unrealized Losses	0
Marketable securities in an unrealized loss position, Fair Value	12,384
Marketable securities in an unrealized loss position, Unrealized Losses	$ (6)