Subsequent Event - Additional Information (Detail) (USD $)	3 Months Ended		1 Months Ended
	Jul. 31, 2013	Jul. 31, 2012	Aug. 14, 2013 Subsequent Event	Aug. 20, 2013 Class A Common Shares Subsequent Event	Aug. 20, 2013 Class B Common Shares Subsequent Event
Subsequent Event [Line Items]
Cash dividends declared per common share	$ 0.00	$ 0.09		$ 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
Purchase price of assets			$ 1,800,000
Purchase price paid in cash			1,200,000
Additional cash payments			$ 200,000