Assumptions Used to Estimate Fair Value of Options and Restricted Stock Using Black-Scholes Option Pricing Model (Detail)	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Dividend yield	0.00%
Stock Options
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Dividend yield	0.00%	0.00%	0.00%
Stock Options | Minimum
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected volatility	54.00%	55.00%	58.00%
Risk-free interest rate	0.83%	1.05%	1.75%
Expected term (in years)	5 years 11 months 9 days	5 years 9 months	6 years
Stock Options | Maximum
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected volatility	55.00%	58.00%	62.00%
Risk-free interest rate	1.40%	2.14%	2.75%
Expected term (in years)	6 years 3 months	6 years 3 months	6 years 3 months
Employee Stock Purchase Plan
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected term (in years)	6 months
Dividend yield	0.00%
Employee Stock Purchase Plan | Minimum
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected volatility	36.00%
Risk-free interest rate	0.10%
Employee Stock Purchase Plan | Maximum
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected volatility	37.00%
Risk-free interest rate	0.11%