Collateral Positions (Details 2) (USD $)	Dec. 31, 2013		Dec. 31, 2012
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	$ 10,219,844,000
U.S. Treasury securities
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	383,743,000
Agency MBS
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	6,158,151,000
Agency MBS | Fannie Mae
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	5,009,406,000
Agency MBS | Freddie Mac
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	1,141,452,000
Agency MBS | Ginnie Mae
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	7,293,000
Non-Agency MBS
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	3,677,950,000	[1],[2],[3]
Non-Agency MBS | Rated AAA
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	14,439,000
Non-Agency MBS | Rated A
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	73,033,000
Non-Agency MBS | Rated BBB
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	65,498,000
Non-Agency MBS | Rated BB
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	75,746,000
Non-Agency MBS | Rated B
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	150,509,000
Non-Agency MBS | Rated CCC
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	388,708,000
Non-Agency MBS | Rated CC
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	85,538,000
Non-Agency MBS | Rated C
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	84,443,000
Non-Agency MBS | Rated D
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	1,051,088,000
Non-Agency MBS | Non Rated
Collateral Positions
Total Fair Value of MBS Pledged and Accrued Interest	1,688,948,000
Repurchase agreements
Collateral Positions
Assets Pledged	10,115,713,000
Amortized Cost	9,296,099,000
Accrued Interest on Pledged MBS	30,082,000
Repurchase agreements | U.S. Treasury securities
Collateral Positions
Assets Pledged	383,743,000
Amortized Cost	383,743,000
Accrued Interest on Pledged MBS	0
Repurchase agreements | Agency MBS
Collateral Positions
Assets Pledged	6,068,447,000
Amortized Cost	6,057,876,000
Accrued Interest on Pledged MBS	15,655,000
Repurchase agreements | Agency MBS | Fannie Mae
Collateral Positions
Assets Pledged	4,941,677,000
Amortized Cost	4,903,089,000
Accrued Interest on Pledged MBS	12,768,000
Repurchase agreements | Agency MBS | Freddie Mac
Collateral Positions
Assets Pledged	1,126,770,000
Amortized Cost	1,154,787,000
Accrued Interest on Pledged MBS	2,887,000
Repurchase agreements | Agency MBS | Ginnie Mae
Collateral Positions
Assets Pledged	0
Amortized Cost	0
Accrued Interest on Pledged MBS	0
Repurchase agreements | Non-Agency MBS
Collateral Positions
Assets Pledged	3,663,523,000	[1],[2],[3]
Amortized Cost	2,854,480,000	[1],[2],[3]
Accrued Interest on Pledged MBS	14,427,000	[1],[2],[3]
Non-Agency MBS acquired from consolidated VIEs in connection with resecuritization transactions	1,885,000,000		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	738,300,000		759,200,000
Repurchase agreements | Non-Agency MBS | Rated AAA
Collateral Positions
Assets Pledged	14,389,000
Amortized Cost	14,062,000
Accrued Interest on Pledged MBS	50,000
Repurchase agreements | Non-Agency MBS | Rated A
Collateral Positions
Assets Pledged	72,811,000
Amortized Cost	66,959,000
Accrued Interest on Pledged MBS	222,000
Repurchase agreements | Non-Agency MBS | Rated BBB
Collateral Positions
Assets Pledged	65,272,000
Amortized Cost	55,828,000
Accrued Interest on Pledged MBS	226,000
Repurchase agreements | Non-Agency MBS | Rated BB
Collateral Positions
Assets Pledged	75,523,000
Amortized Cost	64,098,000
Accrued Interest on Pledged MBS	223,000
Repurchase agreements | Non-Agency MBS | Rated B
Collateral Positions
Assets Pledged	150,119,000
Amortized Cost	131,124,000
Accrued Interest on Pledged MBS	390,000
Repurchase agreements | Non-Agency MBS | Rated CCC
Collateral Positions
Assets Pledged	387,346,000
Amortized Cost	326,517,000
Accrued Interest on Pledged MBS	1,362,000
Repurchase agreements | Non-Agency MBS | Rated CC
Collateral Positions
Assets Pledged	85,219,000
Amortized Cost	72,065,000
Accrued Interest on Pledged MBS	319,000
Repurchase agreements | Non-Agency MBS | Rated C
Collateral Positions
Assets Pledged	84,187,000
Amortized Cost	73,192,000
Accrued Interest on Pledged MBS	256,000
Repurchase agreements | Non-Agency MBS | Rated D
Collateral Positions
Assets Pledged	1,046,134,000
Amortized Cost	925,621,000
Accrued Interest on Pledged MBS	4,954,000
Repurchase agreements | Non-Agency MBS | Non Rated
Collateral Positions
Assets Pledged	1,682,523,000
Amortized Cost	1,125,014,000
Accrued Interest on Pledged MBS	6,425,000
Derivative contracts
Collateral Positions
Assets Pledged	73,859,000
Amortized Cost	73,686,000
Accrued Interest on Pledged MBS	190,000
Derivative contracts | U.S. Treasury securities
Collateral Positions
Assets Pledged	0
Amortized Cost	0
Accrued Interest on Pledged MBS	0
Derivative contracts | Agency MBS
Collateral Positions
Assets Pledged	73,859,000
Amortized Cost	73,686,000
Accrued Interest on Pledged MBS	190,000
Derivative contracts | Agency MBS | Fannie Mae
Collateral Positions
Assets Pledged	54,825,000
Amortized Cost	55,059,000
Accrued Interest on Pledged MBS	136,000
Derivative contracts | Agency MBS | Freddie Mac
Collateral Positions
Assets Pledged	11,752,000
Amortized Cost	11,532,000
Accrued Interest on Pledged MBS	43,000
Derivative contracts | Agency MBS | Ginnie Mae
Collateral Positions
Assets Pledged	7,282,000
Amortized Cost	7,095,000
Accrued Interest on Pledged MBS	11,000
Derivative contracts | Non-Agency MBS
Collateral Positions
Assets Pledged	0	[1],[2],[3]
Amortized Cost	0	[1],[2],[3]
Accrued Interest on Pledged MBS	0	[1],[2],[3]
Derivative contracts | Non-Agency MBS | Rated AAA
Collateral Positions
Assets Pledged	0
Amortized Cost	0
Accrued Interest on Pledged MBS	0
Derivative contracts | Non-Agency MBS | Rated A
Collateral Positions
Assets Pledged	0
Amortized Cost	0
Accrued Interest on Pledged MBS	0
Derivative contracts | Non-Agency MBS | Rated BBB
Collateral Positions
Assets Pledged	0
Amortized Cost	0
Accrued Interest on Pledged MBS	0
Derivative contracts | Non-Agency MBS | Rated BB
Collateral Positions
Assets Pledged	0
Amortized Cost	0
Accrued Interest on Pledged MBS	0
Derivative contracts | Non-Agency MBS | Rated B
Collateral Positions
Assets Pledged	0
Amortized Cost	0
Accrued Interest on Pledged MBS	0
Derivative contracts | Non-Agency MBS | Rated CCC
Collateral Positions
Assets Pledged	0
Amortized Cost	0
Accrued Interest on Pledged MBS	0
Derivative contracts | Non-Agency MBS | Rated CC
Collateral Positions
Assets Pledged	0
Amortized Cost	0
Accrued Interest on Pledged MBS	0
Derivative contracts | Non-Agency MBS | Rated C
Collateral Positions
Assets Pledged	0
Amortized Cost	0
Accrued Interest on Pledged MBS	0
Derivative contracts | Non-Agency MBS | Rated D
Collateral Positions
Assets Pledged	0
Amortized Cost	0
Accrued Interest on Pledged MBS	0
Derivative contracts | Non-Agency MBS | Non Rated
Collateral Positions
Assets Pledged	0
Amortized Cost	0
Accrued Interest on Pledged MBS	$ 0

[1] In addition, $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 December 31, 2013.

[2] Reported based on the lowest rating issued by a Rating Agency, if more than one rating is issued on the security, at the date presented.

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