Declaration of Dividend Payable - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended		1 Months Ended
	Oct. 31, 2013	Oct. 31, 2012	Oct. 31, 2013	Oct. 31, 2012	Aug. 20, 2013 Class A Common Shares	Aug. 20, 2013 Class B Common Shares
Dividends Payable [Line Items]
Cash dividends declared per common share	$ 0.10	$ 0.09	$ 0.10	$ 0.18	$ 0.10	$ 0.10
Cash dividends declared, payment date					Dec. 09, 2013	Dec. 09, 2013
Cash dividends declared, record date					Nov. 15, 2013	Nov. 15, 2013