Stock Repurchases - Additional Information (Detail) (Class A Common Shares, USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended
	Oct. 31, 2013
Equity, Class of Treasury Stock [Line Items]
Common stock shares repurchased	4,444,815
Cost of common stock repurchased	$ 24.3
Shares Stock Repurchase Plan, August 19, 2002
Equity, Class of Treasury Stock [Line Items]
Approved number of shares to be repurchased	2,000,000
Common stock shares repurchased	909,862
Cost of common stock repurchased	$ 4.9