Employee Stock Plans - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended						9 Months Ended				3 Months Ended		9 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2013 Common Stock	Jan. 31, 2012 Common Stock	Jan. 31, 2013 Common Stock	Jan. 31, 2012 Common Stock	Jan. 31, 2013 Employee Stock Purchase Plan	Jan. 31, 2012 Employee Stock Purchase Plan	Jan. 31, 2013 Stock Incentive Plan 2008	Sep. 27, 2012 Stock Incentive Plan 2008	Jan. 31, 2013 Time Based Restricted Stock Minimum	Jan. 31, 2013 Time Based Restricted Stock Maximum	Jan. 31, 2013 Market Based Restricted Stock	Jan. 31, 2013 Stock Options	Jan. 31, 2013 Restricted Stock	Jan. 31, 2012 Restricted Stock	Jan. 31, 2013 Restricted Stock	Jan. 31, 2012 Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average assumptions used to estimate fair value of stock-based compensation, expected volatility				47.07%
Weighted-average assumptions used to estimate fair value of stock-based compensation, risk-free interest rate				1.47%
Weighted-average assumptions used to estimate fair value of stock-based compensation, expected life (in years)				5 years
Weighted-average assumptions used to estimate fair value of stock-based compensation, dividend yield rate				0.00%
Shares available for future issuance									1,600,000			5,700,000
Issuance of full-value stock awards limitation, required ratio to stock option and stock appreciation rights											1.91
Total unrecognized compensation cost related to non-vested awards																$ 900,000	$ 19,800,000		$ 19,800,000
Expected cost recognized over weighted-average period																9 months 18 days			2 years 6 months
Vesting period													3 years	4 years	3 years
Shares repurchased during the period																	2,065	1,151	188,271	184,101
Common stock repurchased, value																	100,000	100,000	2,700,000	4,200,000
Authorized payroll deductions									15.00%
Authorized payroll deductions, value									25,000
Fair market price of common stock									85.00%
Employees stock purchased										76,909
Employees stock purchased, per share value										$ 18.69
Shares reserved for issuance									1,500,000
Amended shares reserved for issuance									3,000,000
Stock issued for stock options exercised					35,083	22,523	170,594	138,709								171,000
Cash proceeds from exercise of stock options	$ 300,000	$ 300,000	$ 1,300,000	$ 2,000,000