Declaration of Dividend Payable - Additional Information (Detail) - $ / shares		3 Months Ended		6 Months Ended
	Aug. 18, 2016	Oct. 31, 2016	Oct. 31, 2015	Oct. 31, 2016	Oct. 31, 2015
Dividends Payable [Line Items]
Cash dividends declared per common share	$ 0.11	$ 0.11	$ 0.10	$ 0.22	$ 0.20
Cash dividend payable date	Dec. 02, 2016
Cash dividends declared, record date	Nov. 11, 2016