Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	$ 1,132,006	$ 1,174,008	$ 1,181,347	$ 1,190,557
Other comprehensive income (loss) before reclassifications	29,878	(16,608)	1,797	(49,143)
Amounts reclassified from accumulated other comprehensive loss	1,120	(210)	1,915	159
Total Other Comprehensive Income (Loss)	30,998	(16,818)	3,712	(48,984)
Balance	1,178,996	1,169,392	1,178,996	1,169,392
Accumulated Other Comprehensive Loss [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(536,024)	(471,746)	(508,738)	(439,580)
Balance	(505,026)	(488,564)	(505,026)	(488,564)
Foreign Currency Translation [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(347,646)	(291,898)	(312,107)	(251,573)
Other comprehensive income (loss) before reclassifications	38,319	(20,424)	2,780	(60,749)
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Total Other Comprehensive Income (Loss)	38,319	(20,424)	2,780	(60,749)
Balance	(309,327)	(312,322)	(309,327)	(312,322)
Unamortized Retirement Costs [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(187,889)	(182,215)	(196,057)	(191,026)
Other comprehensive income (loss) before reclassifications	(7,960)	3,273	(830)	10,993
Amounts reclassified from accumulated other comprehensive loss	1,384	1,114	2,422	2,205
Total Other Comprehensive Income (Loss)	(6,576)	4,387	1,592	13,198
Balance	(194,465)	(177,828)	(194,465)	(177,828)
Interest Rate Swaps [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(489)	2,367	(574)	3,019
Other comprehensive income (loss) before reclassifications	(481)	543	(153)	613
Amounts reclassified from accumulated other comprehensive loss	(264)	(1,324)	(507)	(2,046)
Total Other Comprehensive Income (Loss)	(745)	(781)	(660)	(1,433)
Balance	$ (1,234)	$ 1,586	$ (1,234)	$ 1,586

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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