Collateral Positions (Details) (USD $)	Jun. 30, 2013		Dec. 31, 2012
Collateral Positions
Assets Pledged	$ 10,799,332,000		$ 10,624,276,000
Collateral Held	405,458,000		408,833,000
Repurchase Agreement Borrowings
Collateral Positions
Assets Pledged	10,755,048,000		10,550,345,000
Repurchase Agreement Borrowings | Agency MBS
Collateral Positions
Assets Pledged	6,443,433,000		6,678,384,000
Repurchase Agreement Borrowings | Non-Agency MBS
Collateral Positions
Assets Pledged	3,906,157,000	[1],[2]	3,463,128,000	[1],[2]
Non-Agency MBS acquired from consolidated VIEs	1,935,000,000		1,860,000,000
Non-Agency MBS pledged as collateral in connection with contemporaneous repurchase and reverse repurchase agreements entered into with a single counterparty	740,000,000		759,200,000
Repurchase Agreement Borrowings | U.S. Treasury securities
Collateral Positions
Assets Pledged	405,458,000		408,833,000
Reverse Repurchase Agreements:
Collateral Positions
Collateral Held	405,458,000		408,833,000
Reverse Repurchase Agreements: | U.S. Treasury securities
Collateral Positions
Collateral Held	405,458,000		408,833,000
Derivative contracts
Collateral Positions
Assets Pledged	44,284,000		73,931,000
Derivative contracts | Agency MBS
Collateral Positions
Assets Pledged	41,264,000		68,915,000
Derivative contracts | Cash
Collateral Positions
Assets Pledged	$ 3,020,000	[3]	$ 5,016,000	[3]

[1] Includes $1.935 billion and $1.860 billion of Non-Agency MBS acquired in connection with resecuritization transactions from consolidated VIEs at June 30, 2013 and December 31, 2012, respectively, that are eliminated from the Company’s consolidated balance sheet.

[2] In addition, $740.0 million and $759.2 million of Non-Agency MBS are pledged as collateral in connection with contemporaneous repurchase and reverse repurchase agreements entered into with a single counterparty at June 30, 2013 and December 31, 2012, respectively.

[3] Cash pledged as collateral is reported as “restricted cash” on the Company’s consolidated balance sheet.