Capital Stock and Changes in Capital Accounts, Changes in Common Stock (Details) - shares shares in Thousands	12 Months Ended
	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Class A [Member]
Changes in Common Stock [Abstract]
Number of shares, beginning of year (in shares)	70,166	70,127	70,111
Common stock class conversions (in shares)	42	39	16
Number of shares issued, end of year (in shares)	70,208	70,166	70,127
Changes in Common Stock in Treasury [Abstract]
Number of shares held, beginning of year (in shares)	23,405	22,634	21,853
Purchase of treasury shares (in shares)	308	1,080	1,192
Shares issued under the Director Plan to Directors (in shares)	(6)	(97)	(5)
Restricted shares, forfeited (in shares)	0	1	9
Restricted shares issued from exercise of stock options (in shares)	(60)	(34)	(229)
Shares withheld for taxes (in shares)	129	122	130
Other (in shares)	(1)	(1)	(1)
Number of shares held, end of year (in shares)	23,419	23,405	22,634
Number of Common Stock outstanding, end of year (in shares)	46,789	46,761	47,493
Class A [Member] | Non-PSU Awards [Member]
Changes in Common Stock in Treasury [Abstract]
Restricted shares issued under stock-based compensation plans (in shares)	(268)	(232)	(205)
Class A [Member] | PSU Awards [Member]
Changes in Common Stock in Treasury [Abstract]
Restricted shares issued under stock-based compensation plans (in shares)	(88)	(68)	(110)
Class B [Member]
Changes in Common Stock [Abstract]
Number of shares, beginning of year (in shares)	13,016	13,055	13,071
Common stock class conversions (in shares)	(42)	(39)	(16)
Number of shares issued, end of year (in shares)	12,974	13,016	13,055
Changes in Common Stock in Treasury [Abstract]
Number of shares held, beginning of year (in shares)	3,920	3,918	3,918
Purchase of treasury shares (in shares)	2	2	0
Number of shares held, end of year (in shares)	3,922	3,920	3,918
Number of Common Stock outstanding, end of year (in shares)	9,052	9,096	9,137