Commitments and Contingencies (Rollforward of Reserve for Losses on Repurchases) (Details) (USD $) In Thousands	12 Months Ended
Apr. 30, 2011	Apr. 30, 2010	Apr. 30, 2009	Apr. 30, 2011 Repurchase and Indemnifications [Member]	Apr. 30, 2010 Repurchase and Indemnifications [Member]	Apr. 30, 2009 Repurchase and Indemnifications [Member]	Apr. 30, 2008 Repurchase and Indemnifications [Member]	Apr. 30, 2010 Indemnity Agreement Dated April 2008 [Member]	Apr. 30, 2009 Indemnity Agreement Dated April 2008 [Member]	Apr. 30, 2008 Indemnity Agreement Dated April 2008 [Member]
Reserve for losses on repurchases, beginning balance	$ 188,200	$ 206,595	$ 243,066	$ 126,260	$ 138,415	$ 156,659	$ 193,066	$ 49,785	$ 49,936	$ 50,000
Losses on repurchase and indemnifications	(12,155)	(18,244)	(36,407)
Payments under indemnity agreement dated April 2008	(49,785)	(151)	(64)
Reserve for losses on repurchases, ending balance	$ 126,260	$ 188,200	$ 206,595	$ 126,260	$ 138,415	$ 156,659	$ 193,066	$ 49,785	$ 49,936	$ 50,000

The carrying amount as of the balance sheet date of the combined total of loss contingency liabilities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 5
-Paragraph 9, 10, 11, 12
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6952336&loc=d3e14326-108349

Name:	us-gaap_LossContingencyAccrualAtCarryingValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant