Collateral Positions (Details) (USD $)	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Residential Mortgage-Backed Securities	Mar. 31, 2013 Residential Mortgage-Backed Securities	Dec. 31, 2012 Residential Mortgage-Backed Securities	Jun. 30, 2012 Residential Mortgage-Backed Securities	Jun. 30, 2013 U.S. Treasury securities	Jun. 30, 2013 U.S. Treasury securities Borrowings under repurchase agreement	Jun. 30, 2013 Interest rate swap	Dec. 31, 2012 Interest rate swap	Jun. 30, 2013 Interest rate swap U.S. Treasury securities	Jun. 30, 2013 Interest rate swap and swaption	Mar. 31, 2013 Interest rate swap and swaption	Dec. 31, 2012 Interest rate swap and swaption	Jun. 30, 2012 Interest rate swap and swaption	Jun. 30, 2013 Derivatives	Dec. 31, 2012 Derivatives	Jun. 30, 2013 Agency RMBS Assets pledged for borrowings under repurchase agreements	Dec. 31, 2012 Agency RMBS Assets pledged for borrowings under repurchase agreements	Dec. 31, 2012 Agency RMBS Assets pledged for borrowings under repurchase agreements As Originally Reported	Jun. 30, 2013 Non-Agency RMBS Assets pledged for borrowings under repurchase agreements	Jun. 30, 2013 Cash Assets pledged for borrowings under repurchase agreements	Dec. 31, 2012 Cash Assets pledged for borrowings under repurchase agreements
Collateral Positions
Assets Pledged- Fair Value	$ 4,281,055,000	$ 5,097,966,000
RMBS held by counterparties as security for repurchase agreements	4,146,646,000	5,043,824,000																4,001,774,000	5,043,824,000		144,872,000
Cash collateral	134,409,000	54,142,000							11,200,000	18,200,000						11,177,000	18,160,000					123,232,000	35,982,000
Accrued interest	15,068,000	15,552,000																14,957,000	15,552,000	67,551,000	111,000
Fair Value of Assets Pledged and Accrued Interest, as revised	4,296,123,000	5,113,518,000														11,177,000	18,160,000	4,016,731,000	5,059,376,000		144,983,000	123,232,000	35,982,000
Excess percentage of collateral held over stockholders' equity	5.00%
Collateral received from derivatives counterparties												94,400,000	5,100,000	0	0
Securities received as collateral			1,500,000	3,700,000	2,600,000	5,600,000					94,400,000
Amount posted as collateral							$ 39,800,000	$ 39,800,000