Repurchase Agreements (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013 counterparty		Dec. 31, 2012 counterparty
Information about MBS
Repurchase agreements	$ 8,568,171	[1]	$ 8,752,472	[1]
Number of counterparties	27		26
Threshold percent of stockholders' equity at risk with single counterparty to repurchase agreements or Linked Transactions	5.00%
Repurchase Agreement Borrowings
Information about MBS
Repurchase agreements	8,568,171	[2],[3]	8,752,472	[2]
Weighted Average Interest Rate (as a percent)	0.76%		0.85%
Repurchase Agreement Borrowings | Overnight
Information about MBS
Repurchase agreements	0	[3]
Weighted Average Interest Rate (as a percent)	0.00%
Repurchase Agreement Borrowings | Within 30 days
Information about MBS
Repurchase agreements	6,964,976	[3]
Weighted Average Interest Rate (as a percent)	0.64%
Repurchase Agreement Borrowings | 30 days to 90 days
Information about MBS
Repurchase agreements	1,368,088	[3]
Weighted Average Interest Rate (as a percent)	1.19%
Repurchase Agreement Borrowings | Over 90 days to 12 months
Information about MBS
Repurchase agreements	235,107	[3]
Weighted Average Interest Rate (as a percent)	1.93%
Repurchase Agreement Borrowings | Non-Agency MBS
Information about MBS
Repurchase agreements	2,425,350	[4]	1,988,172	[4]
Linked Transactions | Non-Agency MBS
Information about MBS
Linked repurchase agreements	$ 82,400		$ 35,300

[1] The fair value of securities pledged against the Company’s repurchase agreements was $10.189 billion and $10.550 billion at September 30, 2013 and December 31, 2012, respectively.

[2] At September 30, 2013 and December 31, 2012, the Company had repurchase agreements of $82.4 million and $35.3 million, respectively, that were linked to Non-Agency MBS purchases and accounted for as Linked Transactions, and as such, the linked repurchase agreements are not included in the above table. (See Note 5)

[3] At September 30, 2013, the Company had repurchase agreements of $82.4 million that were linked to Non-Agency MBS purchases and were accounted for as Linked Transactions, and as such, the linked repurchase agreements are not included in the above table. (See Note 5)

[4] Does not reflect Non-Agency MBS and repurchase agreement borrowings that are components of Linked Transactions.