Segment Information, Other Significant Reconciling Items by Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Segment Reporting, Other Significant Reconciling Item [Line Items]
Expenditures for long lived assets	$ (303,025)	$ (151,395)	$ (280,771)
Depreciation and amortization	156,561	155,849	153,925
Operating Segments [Member] | Research [Member]
Segment Reporting, Other Significant Reconciling Item [Line Items]
Expenditures for long lived assets	(160,544)	(31,615)	(9,744)
Depreciation and amortization	29,330	26,410	26,084
Operating Segments [Member] | Publishing [Member]
Segment Reporting, Other Significant Reconciling Item [Line Items]
Expenditures for long lived assets	(31,968)	(37,272)	(39,421)
Depreciation and amortization	43,831	47,108	46,526
Operating Segments [Member] | Solutions [Member]
Segment Reporting, Other Significant Reconciling Item [Line Items]
Expenditures for long lived assets	(8,739)	0	(165,785)
Depreciation and amortization	26,792	22,927	22,644
Corporate/Shared Services [Member]
Segment Reporting, Other Significant Reconciling Item [Line Items]
Expenditures for long lived assets	(101,774)	(82,508)	(65,821)
Depreciation and amortization	$ 56,608	$ 59,404	$ 58,671