Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Segment Reporting Information [Line Items]
Revenue	$ 455,675	$ 436,456	$ 1,318,850	$ 1,266,329
Contribution to profit (loss)	114,174	94,906	299,624	276,971
Operating and administrative expenses	(248,746)	(247,278)	(731,872)	(729,775)
Operating income	67,431	51,160	164,702	142,731
Operating Segments [Member] \| Research [Member]
Segment Reporting Information [Line Items]
Revenue	223,489	205,769	675,986	618,987
Contribution to profit (loss)	59,299	52,508	191,923	173,235
Operating Segments [Member] \| Publishing [Member]
Segment Reporting Information [Line Items]
Revenue	170,244	171,440	466,507	479,701
Contribution to profit (loss)	48,472	38,807	95,957	94,639
Operating Segments [Member] \| Solutions [Member]
Segment Reporting Information [Line Items]
Revenue	61,942	59,247	176,357	167,641
Contribution to profit (loss)	6,403	3,591	11,744	9,097
Corporate [Member]
Segment Reporting Information [Line Items]
Operating and administrative expenses	$ (46,743)	$ (43,746)	$ (134,922)	$ (134,240)

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

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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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