Mortgage Securities And Similar Investments (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 months	Dec. 31, 2010	Dec. 31, 2009
Schedule of Mortgage Securities and Similar Investments [Line Items]
Mortgage securities weighted average contractual maturity, months	289
Number of unsold completed units	7
Amount of securities collateralized	$ 1,800,000
Miscellaneous other revenue (expense) in impairment charges	470,000	106,000	1,200,000
Amount of investment written off			39,200,000
Operating costs	277,000	436,000	37,000
Current-Reset ARMs [Member]
Schedule of Mortgage Securities and Similar Investments [Line Items]
Investments held, basis amount	8,650,000,000
Agency securities average months to roll, months	5.5
Longer-To-Reset ARMs [Member]
Schedule of Mortgage Securities and Similar Investments [Line Items]
Investments held, basis amount	$ 3,370,000,000
Agency securities average months to roll, months	45.1
Minimum [Member]
Schedule of Mortgage Securities and Similar Investments [Line Items]
Agency securities months to roll, months	18
Maximum [Member]
Schedule of Mortgage Securities and Similar Investments [Line Items]
Agency securities months to roll, months	18