Collateral Positions (Details) (USD $)	Mar. 31, 2014		Dec. 31, 2013
Collateral Positions
Assets Pledged	$ 10,578,827,000		$ 10,227,092,000
Collateral Held	435,888,000		383,743,000
Derivative contracts
Collateral Positions
Assets Pledged	103,107,000		111,379,000
Derivative contracts | Agency MBS
Collateral Positions
Assets Pledged	76,968,000		73,859,000
Derivative contracts | Cash
Collateral Positions
Assets Pledged	26,139,000	[1]	37,520,000	[1]
Repurchase Agreement Borrowings
Collateral Positions
Assets Pledged	10,475,720,000		10,115,713,000
Repurchase Agreement Borrowings | Agency MBS
Collateral Positions
Assets Pledged	6,327,835,000		6,068,447,000
Repurchase Agreement Borrowings | Non-Agency MBS
Collateral Positions
Assets Pledged	3,711,997,000	[2],[3]	3,663,523,000	[2],[3]
Non-Agency MBS acquired from consolidated VIEs	1,936,000,000		1,885,000,000
Non-Agency MBS pledged as collateral in connection with contemporaneous repurchase and reverse repurchase agreements entered into with a single counterparty	751,100,000		738,300,000
Repurchase Agreement Borrowings | U.S. Treasury securities
Collateral Positions
Assets Pledged	435,888,000		383,743,000
Reverse Repurchase Agreements:
Collateral Positions
Collateral Held	435,888,000		383,743,000
Reverse Repurchase Agreements: | U.S. Treasury securities
Collateral Positions
Collateral Held	$ 435,888,000		$ 383,743,000

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

[2] In addition, $751.1 million and $738.3 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 March 31, 2014 and December 31, 2013, respectively.

[3] Includes $1.936 billion and $1.885 billion of Non-Agency MBS acquired in connection with resecuritization transactions from consolidated VIEs at March 31, 2014 and December 31, 2013, respectively, that are eliminated from the Company’s consolidated balance sheets.