Commitments And Contingencies (Rollforward Of Reserve For Losses On Repurchases) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Apr. 30, 2011	Jan. 31, 2012 Repurchase And Indemnifications [Member]	Apr. 30, 2011 Repurchase And Indemnifications [Member]	Jan. 31, 2011 Repurchase And Indemnifications [Member]	Apr. 30, 2010 Repurchase And Indemnifications [Member]	Jan. 31, 2011 Indemnity Agreement Dated April 2008 [Member]	Apr. 30, 2010 Indemnity Agreement Dated April 2008 [Member]
Commitments And Contingencies [Line Items]
Reserve for losses on repurchases, beginning balance	$ 126,260	$ 188,200	$ 188,200	$ 142,923	$ 126,260	$ 130,763	$ 138,415	$ 24,223	$ 49,785
Provisions	20,000
Losses on repurchase and indemnifications	(3,337)	(7,652)
Payments under indemnity agreement		(25,562)	49,800
Reserve for losses on repurchases, ending balance	$ 142,923	$ 154,986	$ 126,260	$ 142,923	$ 126,260	$ 130,763	$ 138,415	$ 24,223	$ 49,785