Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	$ 973,745	$ 1,132,006	$ 933,624	$ 1,181,347
Other comprehensive income (loss) before reclassifications	(9,978)	29,878	29,016	1,797
Amounts reclassified from Accumulated Other Comprehensive Loss	2,454	1,120	4,839	1,915
Total Other Comprehensive (Loss) Income	(7,524)	30,998	33,855	3,712
Balance	1,020,213	1,178,996	1,020,213	1,178,996
Accumulated Other Comprehensive Loss [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(534,118)	(536,024)	(575,497)	(508,738)
Balance	(541,642)	(505,026)	(541,642)	(505,026)
Foreign Currency Translation [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(293,850)	(347,646)	(340,703)	(312,107)
Other comprehensive income (loss) before reclassifications	(11,626)	38,319	35,227	2,780
Amounts reclassified from Accumulated Other Comprehensive Loss	0	0	0	0
Total Other Comprehensive (Loss) Income	(11,626)	38,319	35,227	2,780
Balance	(305,476)	(309,327)	(305,476)	(309,327)
Unamortized Retirement Costs [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(233,585)	(187,889)	(227,920)	(196,057)
Other comprehensive income (loss) before reclassifications	1,900	(7,960)	(5,290)	(830)
Amounts reclassified from Accumulated Other Comprehensive Loss	1,503	1,384	3,028	2,422
Total Other Comprehensive (Loss) Income	3,403	(6,576)	(2,262)	1,592
Balance	(230,182)	(194,465)	(230,182)	(194,465)
Interest Rate Swaps [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(6,683)	(489)	(6,874)	(574)
Other comprehensive income (loss) before reclassifications	(252)	(481)	(921)	(153)
Amounts reclassified from Accumulated Other Comprehensive Loss	951	(264)	1,811	(507)
Total Other Comprehensive (Loss) Income	699	(745)	890	(660)
Balance	$ (5,984)	$ (1,234)	$ (5,984)	$ (1,234)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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