Segment Information (Details) $ in Thousands	3 Months Ended	6 Months Ended
Oct. 31, 2016 USD ($)	Oct. 31, 2015 USD ($)	Oct. 31, 2016 USD ($) Segment	Oct. 31, 2015 USD ($)
Segment Information [Abstract]
Number of reportable segments \| Segment			3
Segment Reporting Information [Line Items]
Revenue	$ 425,588	$ 433,362	$ 829,873	$ 856,343
Shared services and administrative costs	(142,796)	(127,873)	(262,600)	(254,442)
Operating income	47,644	60,265	91,571	105,174
Operating Segments [Member]
Segment Reporting Information [Line Items]
Contribution to profit	102,141	100,952	182,065	189,967
Operating Segments [Member] \| Research [Member]
Segment Reporting Information [Line Items]
Revenue	205,994	207,662	413,218	412,364
Contribution to profit	60,292	64,199	120,727	127,413
Operating Segments [Member] \| Publishing [Member]
Segment Reporting Information [Line Items]
Revenue	163,300	176,258	308,261	348,011
Contribution to profit	36,490	34,319	55,832	64,145
Operating Segments [Member] \| Solutions [Member]
Segment Reporting Information [Line Items]
Revenue	56,294	49,442	108,394	95,968
Contribution to profit	5,359	2,434	5,506	(1,591)
Unallocated [Member]
Segment Reporting Information [Line Items]
Shared services and administrative costs	$ (54,497)	$ (40,687)	$ (90,494)	$ (84,793)

Direct contribution to profit minus allocated shared services and administrative costs.

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The aggregate total of expenses of managing and administering the affairs of an entity, including affiliates of the reporting entity, which are not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

+ 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 210.5-03.4)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ 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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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