Earnings Per Common Share - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Oct. 31, 2014	Oct. 31, 2013	Oct. 31, 2014	Oct. 31, 2013
Earnings Per Share [Line Items]
Options to Purchase Excluded	940,630	1,434,477	802,428	1,390,965
Options to Purchase Outstanding	3,079,049	3,281,087	3,079,049	3,281,087
Class A Common Shares
Earnings Per Share [Line Items]
Dividends preference, per share			$ 0.05