Capital Stock and Changes in Capital Accounts (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		6 Months Ended
	Oct. 23, 2019	Jul. 24, 2019	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Cash dividends [Abstract]
Total Dividend					$ 38,486	$ 38,033
Dividend Declared in Q1 2020 [Member]
Cash dividends [Abstract]
Total Dividend		$ 19,200
Dividend Declared in Q2 2020 [Member]
Cash dividends [Abstract]
Total Dividend	$ 19,100
Class A [Member]
Share repurchases [Abstract]
Shares Repurchased (in shares)			334,336	299,188	551,847	425,120
Average Price (in dollars per share)			$ 44.87	$ 56.82	$ 45.30	$ 58.79
Cash dividends [Abstract]
Quarterly Cash Dividend (in dollars per share)			$ 0.34	$ 0.33	$ 0.34	$ 0.33
Changes in Common Stock [Abstract]
Number of shares, beginning of year (in shares)					70,127,000	70,111,000
Common stock class conversions (in shares)					22,000	14,000
Number of shares issued, end of period (in shares)			70,149,000	70,125,000	70,149,000	70,125,000
Changes in Common Stock in Treasury [Abstract]
Number of shares held, beginning of year (in shares)					22,634,000	21,853,000
Purchase of treasury shares (in shares)					552,000	425,000
Restricted shares, forfeited (in shares)					0	0
Restricted shares issued from exercise of stock options (in shares)					(17,000)	(224,000)
Shares withheld for taxes (in shares)					44,000	53,000
Other (in shares)					0	6,000
Number of shares held, end of period (in shares)			23,107,000	22,000,000	23,107,000	22,000,000
Number of Common Stock outstanding, end of period (in shares)			47,042,000	48,125,000	47,042,000	48,125,000
Class A [Member] | Dividend Declared in Q1 2020 [Member]
Cash dividends [Abstract]
Date of Declaration by Board of Directors					Jun. 27, 2019
Quarterly Cash Dividend (in dollars per share)					$ 0.34
Dividend Paid Date					Jul. 24, 2019
Shareholders of Record as of Date					Jul. 10, 2019
Class A [Member] | Dividend Declared in Q2 2020 [Member]
Cash dividends [Abstract]
Date of Declaration by Board of Directors					Sep. 26, 2019
Quarterly Cash Dividend (in dollars per share)					$ 0.34
Dividend Paid Date					Oct. 23, 2019
Shareholders of Record as of Date					Oct. 08, 2019
Class A [Member] | Non-Performance Shares [Member]
Changes in Common Stock in Treasury [Abstract]
Restricted shares issued under stock-based compensation plans (in shares)					(63,000)	(54,000)
Class A [Member] | Performance Share Units [Member]
Changes in Common Stock in Treasury [Abstract]
Restricted shares issued under stock-based compensation plans (in shares)					(43,000)	(59,000)
Class B [Member]
Cash dividends [Abstract]
Quarterly Cash Dividend (in dollars per share)			$ 0.34	$ 0.33	$ 0.34	$ 0.33
Changes in Common Stock [Abstract]
Number of shares, beginning of year (in shares)					13,055,000	13,071,000
Common stock class conversions (in shares)					(22,000)	(14,000)
Number of shares issued, end of period (in shares)			13,033,000	13,057,000	13,033,000	13,057,000
Changes in Common Stock in Treasury [Abstract]
Number of shares held, beginning of year (in shares)					3,918,000	3,918,000
Number of shares held, end of period (in shares)			3,918,000	3,918,000	3,918,000	3,918,000
Number of Common Stock outstanding, end of period (in shares)			9,115,000	9,139,000	9,115,000	9,139,000
Class B [Member] | Dividend Declared in Q1 2020 [Member]
Cash dividends [Abstract]
Date of Declaration by Board of Directors					Jun. 27, 2019
Quarterly Cash Dividend (in dollars per share)					$ 0.34
Dividend Paid Date					Jul. 24, 2019
Shareholders of Record as of Date					Jul. 10, 2019
Class B [Member] | Dividend Declared in Q2 2020 [Member]
Cash dividends [Abstract]
Date of Declaration by Board of Directors					Sep. 26, 2019
Quarterly Cash Dividend (in dollars per share)					$ 0.34
Dividend Paid Date					Oct. 23, 2019
Shareholders of Record as of Date					Oct. 08, 2019