Investments - Schedule of Marketable Securities in Unrealized Loss Position (Detail) $ in Thousands	Jul. 31, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	$ 484,831
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(1,322)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	45,251
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(281)
Marketable securities in an unrealized loss position, Fair Value	530,081
Marketable securities in an unrealized loss position, Unrealized Losses	(1,603)
Corporate notes and obligations
Schedule of Available-for-sale Securities [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	322,777
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(930)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	17,977
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(62)
Marketable securities in an unrealized loss position, Fair Value	340,753
Marketable securities in an unrealized loss position, Unrealized Losses	(992)
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	14,002
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	14,002
Marketable securities in an unrealized loss position, Unrealized Losses	(7)
Mortgage backed obligations
Schedule of Available-for-sale Securities [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	36,878
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(227)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	14,998
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(179)
Marketable securities in an unrealized loss position, Fair Value	51,876
Marketable securities in an unrealized loss position, Unrealized Losses	(406)
Asset backed securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	98,740
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(127)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	6,230
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(23)
Marketable securities in an unrealized loss position, Fair Value	104,970
Marketable securities in an unrealized loss position, Unrealized Losses	(150)
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	8,683
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(27)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	6,046
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(17)
Marketable securities in an unrealized loss position, Fair Value	14,729
Marketable securities in an unrealized loss position, Unrealized Losses	(44)
Foreign government obligations
Schedule of Available-for-sale Securities [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	1,579
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	1,579
Marketable securities in an unrealized loss position, Unrealized Losses	(1)
U.S. agency obligations
Schedule of Available-for-sale Securities [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	2,172
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(3)
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	2,172
Marketable securities in an unrealized loss position, Unrealized Losses	$ (3)