Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	$ 1,169,392	$ 1,047,050	$ 1,190,557	$ 1,003,137
Other comprehensive income (loss) before reclassifications	14,550	42,224	(34,593)	70,381
Amounts reclassified from accumulated other comprehensive loss	(252)	1,324	(93)	3,728
Total Other Comprehensive Income (Loss)	14,298	43,548	(34,686)	74,109
Balance	1,195,429	1,168,326	1,195,429	1,168,326
Accumulated Other Comprehensive Loss [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(488,564)	(476,726)	(439,580)	(507,287)
Balance	(474,266)	(433,178)	(474,266)	(433,178)
Foreign Currency Translation [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(312,322)	(286,171)	(251,573)	(319,212)
Other comprehensive income (loss) before reclassifications	17,515	51,401	(43,234)	84,442
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Total Other Comprehensive Income (Loss)	17,515	51,401	(43,234)	84,442
Balance	(294,807)	(234,770)	(294,807)	(234,770)
Unamortized Retirement Costs [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(177,828)	(193,028)	(191,026)	(190,502)
Other comprehensive income (loss) before reclassifications	(3,141)	(9,686)	7,852	(14,376)
Amounts reclassified from accumulated other comprehensive loss	1,060	1,099	3,265	3,263
Total Other Comprehensive Income (Loss)	(2,081)	(8,587)	11,117	(11,113)
Balance	(179,909)	(201,615)	(179,909)	(201,615)
Interest Rate Swaps [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	1,586	2,473	3,019	2,427
Other comprehensive income (loss) before reclassifications	176	509	789	315
Amounts reclassified from accumulated other comprehensive loss	(1,312)	225	(3,358)	465
Total Other Comprehensive Income (Loss)	(1,136)	734	(2,569)	780
Balance	$ 450	$ 3,207	$ 450	$ 3,207

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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