Summary of Stock Options (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Apr. 30, 2014
$0.00 - $2.86
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 0.00
Exercise Price Upper Range	$ 2.86
Options Outstanding, Number of Options	789
Options Outstanding, Weighted Average Exercise Price	$ 2.04
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	4 years 3 months 22 days
Options Exercisable, Number of Options	766
Exercisable Weighted Average Exercise Price	$ 2.02
$2.96 - $4.85
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 2.96
Exercise Price Upper Range	$ 4.85
Options Outstanding, Number of Options	381
Options Outstanding, Weighted Average Exercise Price	$ 4.36
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	5 years 11 months 23 days
Options Exercisable, Number of Options	377
Exercisable Weighted Average Exercise Price	$ 4.35
$4.86 - $4.86
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 4.86
Exercise Price Upper Range	$ 4.86
Options Outstanding, Number of Options	759
Options Outstanding, Weighted Average Exercise Price	$ 4.86
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	4 years 2 months 9 days
Options Exercisable, Number of Options	714
Exercisable Weighted Average Exercise Price	$ 4.86
$5.35 - $6.54
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 5.35
Exercise Price Upper Range	$ 6.54
Options Outstanding, Number of Options	725
Options Outstanding, Weighted Average Exercise Price	$ 6.40
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	8 years 1 month 6 days
Options Exercisable, Number of Options	333
Exercisable Weighted Average Exercise Price	$ 6.31
$6.58 - $7.32
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 6.58
Exercise Price Upper Range	$ 7.32
Options Outstanding, Number of Options	733
Options Outstanding, Weighted Average Exercise Price	$ 7.08
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	8 years 11 months 16 days
Options Exercisable, Number of Options	195
Exercisable Weighted Average Exercise Price	$ 6.82
$7.39 - $7.50
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 7.39
Exercise Price Upper Range	$ 7.50
Options Outstanding, Number of Options	759
Options Outstanding, Weighted Average Exercise Price	$ 7.41
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	8 years 9 months 18 days
Options Exercisable, Number of Options	88
Exercisable Weighted Average Exercise Price	$ 7.39
$7.51 - $9.46
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 7.51
Exercise Price Upper Range	$ 9.46
Options Outstanding, Number of Options	815
Options Outstanding, Weighted Average Exercise Price	$ 8.88
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	7 years 11 months 9 days
Options Exercisable, Number of Options	300
Exercisable Weighted Average Exercise Price	$ 8.72
$9.51 - $9.60
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 9.51
Exercise Price Upper Range	$ 9.60
Options Outstanding, Number of Options	713
Options Outstanding, Weighted Average Exercise Price	$ 9.53
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	7 years 11 months 5 days
Options Exercisable, Number of Options	133
Exercisable Weighted Average Exercise Price	$ 9.59
$10.24 - $12.60
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 10.24
Exercise Price Upper Range	$ 12.60
Options Outstanding, Number of Options	843
Options Outstanding, Weighted Average Exercise Price	$ 11.91
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	6 years 2 months 16 days
Options Exercisable, Number of Options	473
Exercisable Weighted Average Exercise Price	$ 12.24
$13.95 - $18.67
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 13.95
Exercise Price Upper Range	$ 18.67
Options Outstanding, Number of Options	574
Options Outstanding, Weighted Average Exercise Price	$ 14.64
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	7 years 8 months 23 days
Options Exercisable, Number of Options	279
Exercisable Weighted Average Exercise Price	$ 14.74
$0.00 - $18.67
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$ 0.00
Exercise Price Upper Range	$ 18.67
Options Outstanding, Number of Options	7,091
Options Outstanding, Weighted Average Exercise Price	$ 7.74
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	7 years 7 days
Options Exercisable, Number of Options	3,658
Exercisable Weighted Average Exercise Price	$ 6.71