Mortgage-Backed Securities (Schedule Of Agency MBS Forward Purchase Commitments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012
Mortgage-Backed Securities [Abstract]
Days to coupon reset or contractual payment, minimum range	30
Days to coupon reset or contractual payment, maximum range	90
Forward Purchase agreements - Face	$ 1,750,659
Forward Purchase agreements - Cost	1,812,203
Forward Purchase agreements - Fair Market Value	1,815,658
Forward Purchase agreements - Due To Brokers	1,812,203	[1]
Forward Purchase agreements - Net Asset	$ 3,455

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