Mortgage-Backed Securities (Schedule Of Agency MBS Forward Purchase Commitments) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 days
Mortgage-Backed Securities [Abstract]
Forward purchase agreements - Face	$ 340,000
Forward purchase agreements - Cost	348,937
Forward purchase agreements - Fair Market Value	351,249
Forward purchase agreements - Due To Brokers	348,937	[1]
Forward purchase agreements - Net Asset	$ 2,312
Minimum number of days to settle the amount to brokers	30
Maximum number of days to settle the amount to brokers	90

[1] Amounts due to brokers are usually settled within 30-90 days after period end.