Schedule Of Interest Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Gain Loss On Investments Including Marketable Securities And Investments Held At Cost Income Statement Reported Amounts Summary [Line Items]
Coupon interest on MBS									$ 616,632	$ 667,644	$ 518,048
Net premium amortization									(165,924)	(162,844)	(93,335)
Interest income on mortgage-backed securities	$ 104,312	$ 107,040	$ 115,115	$ 124,241	$ 131,381	$ 131,940	$ 128,720	$ 112,759	$ 450,708	$ 504,800	$ 424,713