Earnings Per Common Share - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2015	Jan. 31, 2014
Earnings Per Share [Line Items]
Options to Purchase Excluded	952,761	440,196	847,539	979,764
Options to Purchase Outstanding	3,056,335	3,223,966	3,056,335	3,223,966
Class A Common Shares
Earnings Per Share [Line Items]
Dividends preference, per share			0.05