Goodwill and Intangible Assets, Goodwill (Details) - USD ($) $ in Thousands	6 Months Ended
Oct. 31, 2017	Oct. 31, 2016
Goodwill [Roll Forward]
Beginning balance	$ 982,101	$ 951,663
Acquisitions		78,224
Foreign translation adjustment	17,445	(55,819)
Ending balance	999,546	974,068
Research [Member]
Goodwill [Roll Forward]
Beginning balance	437,928	406,395
Acquisitions		74,119
Foreign translation adjustment	9,569	(51,110)
Ending balance	447,497	429,404
Publishing [Member]
Goodwill [Roll Forward]
Beginning balance	283,192	284,217
Acquisitions		0
Foreign translation adjustment	7,876	(4,709)
Ending balance	291,068	279,508
Solutions [Member]
Goodwill [Roll Forward]
Beginning balance	260,981	261,051
Acquisitions		4,105
Foreign translation adjustment	0	0
Ending balance	$ 260,981	$ 265,156

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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- Definition

Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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