Common Shares (Details) - shares	6 Months Ended
	Oct. 31, 2016	Apr. 30, 2016	Mar. 23, 2015
Stockholders' Equity Note [Abstract]
Stock Repurchased During Period, Shares	0
Common Shares Information
Common shares authorized	300,000,000	300,000,000
Common shares outstanding	116,435,507	116,306,894	120,000,000
Treasury shares	30,062,223	30,190,836
Common Shares (Additional Textual) [Abstract]
Shares remaining for repurchase	6,600,000