Segment Information, Revenues from External Customers and Long-Lived Assets by Geography Area (Details) - USD ($) $ in Thousands	12 Months Ended
Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 1,718,530	$ 1,727,037	$ 1,822,440
Long-lived assets	252,488	214,770	193,010
Pretax income for consolidated operations outside the United States	192,910	159,152	165,085
Reportable Geographical Components [Member] \| United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	786,574	884,185	920,166
Long-lived assets	208,572	166,878	143,786
Reportable Geographical Components [Member] \| United States [Member] \| Export Sales [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	148,700	164,400	168,000
Reportable Geographical Components [Member] \| United Kingdom [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	189,479	153,442	142,680
Long-lived assets	21,368	23,246	24,711
Reportable Geographical Components [Member] \| Germany [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	75,090	69,676	83,714
Long-lived assets	8,770	9,629	9,781
Reportable Geographical Components [Member] \| Japan [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	62,674	76,930	84,420
Long-lived assets	75	35	21
Reportable Geographical Components [Member] \| China [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	39,653	52,815	45,159
Long-lived assets	270	244	307
Reportable Geographical Components [Member] \| India [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	34,306	38,208	39,494
Long-lived assets	245	234	180
Reportable Geographical Components [Member] \| Australia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	66,309	78,786	80,380
Long-lived assets	591	1,041	1,696
Reportable Geographical Components [Member] \| France [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	44,760	49,970	57,492
Long-lived assets	9,765	9,517	6,720
Reportable Geographical Components [Member] \| Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	50,740	50,243	56,949
Long-lived assets	1,232	1,617	1,606
Reportable Geographical Components [Member] \| Other Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	368,945	272,782	311,986
Long-lived assets	$ 1,600	$ 2,329	$ 4,202

The portion of earnings or loss from continuing operations before income taxes that is attributable to foreign operations, which is defined as Income or Loss generated from operations located outside the entity's country of domicile.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h)(1)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e9038-108599

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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