Common Shares (Details) - shares	Jan. 31, 2016	Apr. 30, 2015	Mar. 23, 2015
Common Shares Information
Common shares authorized	300,000,000	300,000,000
Common shares outstanding	119,685,003	119,577,333	120,000,000
Treasury shares	26,812,727	26,920,397
Common Shares (Additional Textual) [Abstract]
Shares remaining for repurchase	10,000,000