Accumulated Other Comprehensive Income (Components Of Accumulated Other Comprehensive Income) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Accumulated Other Comprehensive Income [Abstract]
Unrealized gain on agency securities, net	$ 385,101		$ 162,312
Unrealized gain (loss) on unsettled securities	631		(64)
Unrealized loss on short term investment	(287)	[1]	(136)	[1]
Unrealized loss on derivative instruments	(212,123)		(56,221)
Accumulated other comprehensive income	173,322		105,891
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Net of Tax	$ 20,576		$ 13,551

[1] This line item is included in other assets on the balance sheet.