Consolidated Balance Sheets (Parenthetical) - shares	Apr. 30, 2020	Apr. 30, 2019
Statement of Financial Position [Abstract]
Serial preferred shares, no par value, shares authorized (in shares)	6,000,000	6,000,000
Serial preferred shares, no par value, shares outstanding (in shares)	0	0
Common shares, no par value, shares authorized (in shares)	300,000,000	300,000,000
Common shares, no par value, shares outstanding (in shares)	114,072,726	113,742,296
Treasury shares, shares outstanding (in shares)	32,425,004	32,755,434