Investments - Schedule of Marketable Securities in Unrealized Loss Position (Detail) $ in Thousands	Apr. 30, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	$ 517,640
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(1,226)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	83,204
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(554)
Marketable securities in an unrealized loss position, Fair Value	600,844
Marketable securities in an unrealized loss position, Unrealized Losses	(1,780)
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	272,239
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(813)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	61,847
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(464)
Marketable securities in an unrealized loss position, Fair Value	334,086
Marketable securities in an unrealized loss position, Unrealized Losses	(1,277)
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	47,552
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(39)
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	47,552
Marketable securities in an unrealized loss position, Unrealized Losses	(39)
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	52,427
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(126)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	8,986
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(48)
Marketable securities in an unrealized loss position, Fair Value	61,413
Marketable securities in an unrealized loss position, Unrealized Losses	(174)
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	106,226
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(148)
Marketable securities in an unrealized loss position for more than 12 months, Fair Value	12,371
Marketable securities in an unrealized loss position for more than 12 months, Unrealized Losses	(42)
Marketable securities in an unrealized loss position, Fair Value	118,597
Marketable securities in an unrealized loss position, Unrealized Losses	(190)
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities in an unrealized loss position for less than 12 months, Fair Value	18,065
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(86)
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	18,065
Marketable securities in an unrealized loss position, Unrealized Losses	(86)
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	7,650
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	7,650
Marketable securities in an unrealized loss position, Unrealized Losses	(3)
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	13,481
Marketable securities in an unrealized loss position for less than 12 months, Unrealized Losses	(11)
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	13,481
Marketable securities in an unrealized loss position, Unrealized Losses	$ (11)