Summary of Stock Options (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Apr. 30, 2013
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Number of Options	10,829
Options Outstanding, Weighted Average Exercise Price	$ 6.83
Options Outstanding, Weighted Average Remaining Contractual Life	7 years 8 months 23 days
Options Exercisable, Number of Options	5,481
Options Exercisable, Weighted Average Exercise Price	$ 4.12
Options Exercisable, Weighted Average Remaining Contractual Life	6 years 6 months 22 days
Range One
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 0.00
Exercise Price Upper Range	$ 0.03
Options Outstanding, Number of Options	47
Options Outstanding, Weighted Average Exercise Price	$ 0.00
Options Outstanding, Weighted Average Remaining Contractual Life	2 years 1 month 17 days
Options Exercisable, Number of Options	47
Options Exercisable, Weighted Average Exercise Price	$ 0.00
Options Exercisable, Weighted Average Remaining Contractual Life	2 years 1 month 17 days
Range Two
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 0.03
Exercise Price Upper Range	$ 0.12
Options Outstanding, Number of Options	66
Options Outstanding, Weighted Average Exercise Price	$ 0.05
Options Outstanding, Weighted Average Remaining Contractual Life	2 years 9 months 26 days
Options Exercisable, Number of Options	66
Options Exercisable, Weighted Average Exercise Price	$ 0.05
Options Exercisable, Weighted Average Remaining Contractual Life	2 years 9 months 26 days
Range Three
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 0.16
Exercise Price Upper Range	$ 0.49
Options Outstanding, Number of Options	110
Options Outstanding, Weighted Average Exercise Price	$ 0.30
Options Outstanding, Weighted Average Remaining Contractual Life	3 years 4 months 10 days
Options Exercisable, Number of Options	110
Options Exercisable, Weighted Average Exercise Price	$ 0.30
Options Exercisable, Weighted Average Remaining Contractual Life	3 years 4 months 10 days
Range Four
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 0.84
Exercise Price Upper Range	$ 1.83
Options Outstanding, Number of Options	350
Options Outstanding, Weighted Average Exercise Price	$ 1.80
Options Outstanding, Weighted Average Remaining Contractual Life	4 years 7 months 21 days
Options Exercisable, Number of Options	350
Options Exercisable, Weighted Average Exercise Price	$ 1.80
Options Exercisable, Weighted Average Remaining Contractual Life	4 years 7 months 21 days
Range Five
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 2.17
Exercise Price Upper Range	$ 4.13
Options Outstanding, Number of Options	2,778
Options Outstanding, Weighted Average Exercise Price	$ 2.81
Options Outstanding, Weighted Average Remaining Contractual Life	6 years 2 months 9 days
Options Exercisable, Number of Options	2,534
Options Exercisable, Weighted Average Exercise Price	$ 2.79
Options Exercisable, Weighted Average Remaining Contractual Life	6 years 29 days
Range Six
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 4.20
Exercise Price Upper Range	$ 6.54
Options Outstanding, Number of Options	2,932
Options Outstanding, Weighted Average Exercise Price	$ 5.14
Options Outstanding, Weighted Average Remaining Contractual Life	7 years 9 months 22 days
Options Exercisable, Number of Options	1,631
Options Exercisable, Weighted Average Exercise Price	$ 4.78
Options Exercisable, Weighted Average Remaining Contractual Life	7 years 4 months 10 days
Range Seven
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 6.58
Exercise Price Upper Range	$ 12.00
Options Outstanding, Number of Options	2,694
Options Outstanding, Weighted Average Exercise Price	$ 9.28
Options Outstanding, Weighted Average Remaining Contractual Life	8 years 11 months 1 day
Options Exercisable, Number of Options	712
Options Exercisable, Weighted Average Exercise Price	$ 9.20
Options Exercisable, Weighted Average Remaining Contractual Life	8 years 5 months 5 days
Range Eight
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 12.60
Exercise Price Upper Range	$ 18.67
Options Outstanding, Number of Options	1,852
Options Outstanding, Weighted Average Exercise Price	$ 13.70
Options Outstanding, Weighted Average Remaining Contractual Life	9 years 4 months 13 days
Options Exercisable, Number of Options	31
Options Exercisable, Weighted Average Exercise Price	$ 16.82
Options Exercisable, Weighted Average Remaining Contractual Life	9 years