Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2020	Jan. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	$ 1,178,996	$ 1,169,392	$ 1,181,347	$ 1,190,557
Other comprehensive income (loss) before reclassifications	5,561	14,550	7,358	(34,593)
Amounts reclassified from accumulated other comprehensive loss	1,125	(252)	3,040	(93)
Total Other Comprehensive Income (Loss)	6,686	14,298	10,398	(34,686)
Balance	1,197,235	1,195,429	1,197,235	1,195,429
Accumulated Other Comprehensive Loss [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(505,026)	(488,564)	(508,738)	(439,580)
Balance	(498,340)	(474,266)	(498,340)	(474,266)
Foreign Currency Translation [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(309,327)	(312,322)	(312,107)	(251,573)
Other comprehensive income (loss) before reclassifications	7,895	17,515	10,675	(43,234)
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Total Other Comprehensive Income (Loss)	7,895	17,515	10,675	(43,234)
Balance	(301,432)	(294,807)	(301,432)	(294,807)
Unamortized Retirement Costs [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(194,465)	(177,828)	(196,057)	(191,026)
Other comprehensive income (loss) before reclassifications	(2,063)	(3,141)	(2,893)	7,852
Amounts reclassified from accumulated other comprehensive loss	1,247	1,060	3,669	3,265
Total Other Comprehensive Income (Loss)	(816)	(2,081)	776	11,117
Balance	(195,281)	(179,909)	(195,281)	(179,909)
Interest Rate Swaps [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(1,234)	1,586	(574)	3,019
Other comprehensive income (loss) before reclassifications	(271)	176	(424)	789
Amounts reclassified from accumulated other comprehensive loss	(122)	(1,312)	(629)	(3,358)
Total Other Comprehensive Income (Loss)	(393)	(1,136)	(1,053)	(2,569)
Balance	$ (1,627)	$ 450	$ (1,627)	$ 450

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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