Goodwill and Intangible Assets (Details) (USD $)	12 Months Ended
	Apr. 30, 2012	Apr. 30, 2011
Goodwill [Roll Forward]
Beginning balance	$ 642,898,000
Acquisitions	56,847,000
Foreign translation adjustment	(9,126,000)
Ending balance	690,619,000
Finite-Lived Intangible Assets [Line Items]
Intangible assets with determinable lives, at cost	901,627,000	862,428,000
Intangible assets with determinable lives, accumulated amortization	(254,059,000)	(216,799,000)
Total intangible assets [Abstract]
Total intangible assets, at cost	1,169,554,000	1,149,529,000
Estimated future amortization expense related to intangible assets [Abstract]
2013	40,700,000
2014	38,000,000
2015	32,000,000
2016	30,600,000
2017	29,400,000
Content and Publishing Rights [Member]
Indefinite-lived Intangible Assets by Major Class [Line Items]
Intangible assets with indefinite lives, at cost	102,031,000	111,908,000
Brands and Trademarks [Member]
Indefinite-lived Intangible Assets by Major Class [Line Items]
Intangible assets with indefinite lives, at cost	165,896,000	175,193,000
Content and Publishing Rights [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets with determinable lives, at cost	794,986,000	779,135,000
Intangible assets with determinable lives, accumulated amortization	(227,934,000)	(195,586,000)
Brands and Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets with determinable lives, at cost	22,374,000	18,814,000
Intangible assets with determinable lives, accumulated amortization	(8,401,000)	(6,944,000)
Covenants not to Compete [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets with determinable lives, at cost	790,000	350,000
Intangible assets with determinable lives, accumulated amortization	(484,000)	(297,000)
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets with determinable lives, at cost	83,477,000	64,129,000
Intangible assets with determinable lives, accumulated amortization	(17,240,000)	(13,972,000)
STMS [Member]
Goodwill [Roll Forward]
Beginning balance	483,433,000
Acquisitions	0
Foreign translation adjustment	(8,856,000)
Ending balance	474,577,000
Professional and Trade [Member]
Goodwill [Roll Forward]
Beginning balance	159,465,000
Acquisitions	56,847,000
Foreign translation adjustment	(270,000)
Ending balance	$ 216,042,000