Investments - Schedule of Marketable Securities in Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Oct. 31, 2014
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	$ 341,045
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(852)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	7,032
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(55)
Marketable securities in an unrealized loss position, Fair Value	348,077
Marketable securities in an unrealized loss position, Unrealized Losses	(907)
Corporate notes and obligations
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	206,762
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(410)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	3,276
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(29)
Marketable securities in an unrealized loss position, Fair Value	210,038
Marketable securities in an unrealized loss position, Unrealized Losses	(439)
U.S. treasury securities
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	25,671
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(28)
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	25,671
Marketable securities in an unrealized loss position, Unrealized Losses	(28)
Mortgage backed obligations
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	30,652
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(281)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	1,399
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(21)
Marketable securities in an unrealized loss position, Fair Value	32,051
Marketable securities in an unrealized loss position, Unrealized Losses	(302)
Asset backed securities
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	45,589
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(38)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	2,357
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(5)
Marketable securities in an unrealized loss position, Fair Value	47,946
Marketable securities in an unrealized loss position, Unrealized Losses	(43)
Municipal securities
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	22,391
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(79)
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	22,391
Marketable securities in an unrealized loss position, Unrealized Losses	(79)
U.S. agency obligations
Investment Holdings [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	9,980
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(16)
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	9,980
Marketable securities in an unrealized loss position, Unrealized Losses	$ (16)