Contingencies And Other Disclosures (Schedule Of Original Purchase Amount Of Investments Subject To Litigation) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012
Alt-A [Member] | Senior [Member]
Loss Contingencies [Line Items]
Original purchase amounts of the investments at issue	$ 978,938
Alt-A [Member] | 2005 [Member] | Senior [Member]
Loss Contingencies [Line Items]
Original purchase amounts of the investments at issue	743,868	[1]
Alt-A [Member] | 2006 [Member] | Senior [Member]
Loss Contingencies [Line Items]
Original purchase amounts of the investments at issue	230,020	[1]
Alt-A [Member] | 2007 [Member] | Senior [Member]
Loss Contingencies [Line Items]
Original purchase amounts of the investments at issue	5,050
Jumbo [Member] | Senior [Member]
Loss Contingencies [Line Items]
Original purchase amounts of the investments at issue	194,659
Jumbo [Member] | Junior [Member]
Loss Contingencies [Line Items]
Original purchase amounts of the investments at issue	16,877
Jumbo [Member] | 2005 [Member] | Senior [Member]
Loss Contingencies [Line Items]
Original purchase amounts of the investments at issue	60,000	[1]
Jumbo [Member] | 2006 [Member] | Senior [Member]
Loss Contingencies [Line Items]
Original purchase amounts of the investments at issue	84,659	[1]
Jumbo [Member] | 2006 [Member] | Junior [Member]
Loss Contingencies [Line Items]
Original purchase amounts of the investments at issue	9,793	[1]
Jumbo [Member] | 2007 [Member] | Senior [Member]
Loss Contingencies [Line Items]
Original purchase amounts of the investments at issue	50,000
Jumbo [Member] | 2007 [Member] | Junior [Member]
Loss Contingencies [Line Items]
Original purchase amounts of the investments at issue	7,084
Federal Housing Finance Agency [Member] | Senior [Member]
Loss Contingencies [Line Items]
Original purchase amounts of the investments at issue	$ 643,751

[1] The amounts shown in the table which are the subject of the FHFA litigations include all of the Senior Atl-A loans from 2006 and $643,751 of the Senior Alt-A from 2005.