Schedule of Marketable Securities in Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2013
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	$ 125,416
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(660)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	6,070
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(77)
Marketable securities in an unrealized loss position, Fair Value	131,486
Marketable securities in an unrealized loss position, Unrealized Losses	(737)
Corporate Notes and Other Obligations
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	64,569
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(377)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	3,013
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(44)
Marketable securities in an unrealized loss position, Fair Value	67,582
Marketable securities in an unrealized loss position, Unrealized Losses	(421)
US Treasury Securities
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	620
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(1)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	0
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	0
Marketable securities in an unrealized loss position, Fair Value	620
Marketable securities in an unrealized loss position, Unrealized Losses	(1)
Mortgage Backed Obligations
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	13,781
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(94)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	3,057
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(33)
Marketable securities in an unrealized loss position, Fair Value	16,838
Marketable securities in an unrealized loss position, Unrealized Losses	(127)
Asset Backed Securities
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	16,724
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(98)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	0
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	0
Marketable securities in an unrealized loss position, Fair Value	16,724
Marketable securities in an unrealized loss position, Unrealized Losses	(98)
Municipal Securities
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	996
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(4)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	0
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	0
Marketable securities in an unrealized loss position, Fair Value	996
Marketable securities in an unrealized loss position, Unrealized Losses	(4)
Foreign Government Obligations
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	14,833
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(7)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	0
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	0
Marketable securities in an unrealized loss position, Fair Value	14,833
Marketable securities in an unrealized loss position, Unrealized Losses	(7)
US Agency Obligations
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	10,138
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(75)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	0
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	0
Marketable securities in an unrealized loss position, Fair Value	10,138
Marketable securities in an unrealized loss position, Unrealized Losses	(75)
Covered Bonds
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	3,755
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(4)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	0
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	0
Marketable securities in an unrealized loss position, Fair Value	3,755
Marketable securities in an unrealized loss position, Unrealized Losses	$ (4)