Stockholders' Equity - Additional Information (Detail) (USD $)	0 Months Ended	9 Months Ended		13 Months Ended	89 Months Ended
	Feb. 01, 2006	Oct. 31, 2014	Oct. 31, 2013	Jul. 31, 2014	Jul. 03, 2013	Jan. 31, 2014	Oct. 31, 2014 2014 Inducement Equity Incentive Plan	Jul. 10, 2014 2014 Inducement Equity Incentive Plan	Jul. 09, 2014 2006 Inducement Equity Incentive Plan [Member]	Oct. 31, 2014 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized (in shares)								335,000
Shares available for grant (in shares)		49,291,897				55,852,536	176,046		319,000	4,298,711
Amount withheld on behalf of employees for future purchases										$ 60,700,000
Contractual life of stock options (in years)	10 years			7 years	5 years
Total intrinsic value of the options exercised during the period		202,000,000	218,000,000
Weighted-average remaining contractual life of vested and expected to vest options (in years)		3 years 9 months 18 days
Options vested		10,185,611
Weighted average exercise price vested		$ 31.18
Weighted-average contractual life of vested and expected to vest options (in years)		2 years 2 months 1 day
Aggregate intrinsic value		$ 334,162,000
Weighted-average exercise price		$ 0.001
Restricted stock units, vesting period (in years)		4 years
Weighted-average grant date fair value of the restricted stock units issued		$ 58.84	$ 43.52