Residential Mortgage Investments (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012 M	Mar. 31, 2011	Dec. 31, 2009
Schedule Of Residential Mortgage Investments [Line Items]
Mortgage securities weighted average contractual maturity, months	291
Number of unsold completed units	7
Amount of securities collateralized	$ 1,800,000
Operating costs	101,000	103,000
Amount of investment written off			39,200,000
Current-Reset ARMs [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Investments held, basis amount	8,550,000,000
Agency securities average months to roll, months	5.2
Longer-To-Reset ARMs [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Investments held, basis amount	$ 4,180,000,000
Agency securities average months to roll, months	45.7
Minimum [Member] | Current-Reset ARMs [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Agency securities months to roll	18
Maximum [Member] | Longer-To-Reset ARMs [Member]
Schedule Of Residential Mortgage Investments [Line Items]
Agency securities months to roll	18