Subsequent Event (Details) (Financing [Member], USD $) In Millions, unless otherwise specified	6 Months Ended
	Oct. 31, 2011
Financing [Member]
Subsequent Event [Line Items]
Amount of credit agreement	$ 800
Credit Agreement, Expiration Date	2016-11-18
Prior Credit Agreement, Expiration Date	April 2012
Credit Agreement, Restrictive Covenant	Ratio of consolidated EBITDA (as defined in the agreement) to consolidated interest expense of at least 3 to 1.