Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance			$ 1,003,137
Other comprehensive income (loss) before reclassifications	$ 4,201	$ (8,798)	28,157	$ (44,873)
Amounts reclassified from accumulated other comprehensive loss	1,263	6,301	2,404	5,910
Total Other Comprehensive Income (Loss)	5,464	(2,497)	30,561	(38,963)
Balance	1,047,050	981,501	1,047,050	981,501
Accumulated Other Comprehensive Loss [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(482,190)	(484,152)	(507,287)	(447,686)
Balance	(476,726)	(486,649)	(476,726)	(486,649)
Foreign Currency Translation [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(291,807)	(312,560)	(319,212)	(267,920)
Other comprehensive income (loss) before reclassifications	5,636	(25,824)	33,041	(70,464)
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Total Other Comprehensive Income (Loss)	5,636	(25,824)	33,041	(70,464)
Balance	(286,171)	(338,384)	(286,171)	(338,384)
Unamortized Retirement Costs [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(192,449)	(170,401)	(190,502)	(179,405)
Other comprehensive income (loss) before reclassifications	(1,673)	15,826	(4,690)	25,494
Amounts reclassified from accumulated other comprehensive loss	1,094	6,325	2,164	5,661
Total Other Comprehensive Income (Loss)	(579)	22,151	(2,526)	31,155
Balance	(193,028)	(148,250)	(193,028)	(148,250)
Interest Rate Swaps [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	2,066	(1,191)	2,427	(361)
Other comprehensive income (loss) before reclassifications	238	1,200	(194)	97
Amounts reclassified from accumulated other comprehensive loss	169	(24)	240	249
Total Other Comprehensive Income (Loss)	407	1,176	46	346
Balance	$ 2,473	$ (15)	$ 2,473	$ (15)

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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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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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