Collateral Positions (Details 2) (USD $)	Sep. 30, 2014		Dec. 31, 2013
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	$ 9,689,421,000
Non-Agency Mortgage Backed Securities
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	3,467,122,000	[1],[2]
U.S. Treasury securities
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	442,370,000
Agency Mortgage Backed Securities
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	5,779,929,000
Agency Mortgage Backed Securities | Fannie Mae
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	4,762,647,000
Agency Mortgage Backed Securities | Freddie Mac
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	1,011,006,000
Agency Mortgage Backed Securities | Ginnie Mae
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	6,276,000
Securities Sold under Agreements to Repurchase
Collateral Positions
Fair Value/ Carrying Value	9,595,270,000
Amortized Cost	8,720,162,000
Accrued Interest on Pledged MBS	26,569,000
Securities Sold under Agreements to Repurchase | Non-Agency Mortgage Backed Securities
Collateral Positions
Fair Value/ Carrying Value	3,454,698,000	[1],[2]
Amortized Cost	2,632,613,000	[1],[2]
Accrued Interest on Pledged MBS	12,424,000	[1],[2]
Non-Agency MBS acquired from consolidated VIEs in connection with resecuritization transactions	1,276,000,000		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	736,800,000		738,300,000
Securities Sold under Agreements to Repurchase | U.S. Treasury securities
Collateral Positions
Fair Value/ Carrying Value	442,370,000
Amortized Cost	442,370,000
Accrued Interest on Pledged MBS	0
Securities Sold under Agreements to Repurchase | Agency Mortgage Backed Securities
Collateral Positions
Fair Value/ Carrying Value	5,698,202,000
Amortized Cost	5,645,179,000
Accrued Interest on Pledged MBS	14,145,000
Securities Sold under Agreements to Repurchase | Agency Mortgage Backed Securities | Fannie Mae
Collateral Positions
Fair Value/ Carrying Value	4,744,666,000
Amortized Cost	4,682,097,000
Accrued Interest on Pledged MBS	11,763,000
Securities Sold under Agreements to Repurchase | Agency Mortgage Backed Securities | Freddie Mac
Collateral Positions
Fair Value/ Carrying Value	953,536,000
Amortized Cost	963,082,000
Accrued Interest on Pledged MBS	2,382,000
Securities Sold under Agreements to Repurchase | Agency Mortgage Backed Securities | Ginnie Mae
Collateral Positions
Fair Value/ Carrying Value	0
Amortized Cost	0
Accrued Interest on Pledged MBS	0
Derivative contracts
Collateral Positions
Fair Value/ Carrying Value	67,431,000
Amortized Cost	68,007,000
Accrued Interest on Pledged MBS	151,000
Derivative contracts | Non-Agency Mortgage Backed Securities
Collateral Positions
Fair Value/ Carrying Value	0	[1],[2]
Amortized Cost	0	[1],[2]
Accrued Interest on Pledged MBS	0	[1],[2]
Derivative contracts | U.S. Treasury securities
Collateral Positions
Fair Value/ Carrying Value	0
Amortized Cost	0
Accrued Interest on Pledged MBS	0
Derivative contracts | Agency Mortgage Backed Securities
Collateral Positions
Fair Value/ Carrying Value	67,431,000
Amortized Cost	68,007,000
Accrued Interest on Pledged MBS	151,000
Derivative contracts | Agency Mortgage Backed Securities | Fannie Mae
Collateral Positions
Fair Value/ Carrying Value	6,205,000
Amortized Cost	5,965,000
Accrued Interest on Pledged MBS	13,000
Derivative contracts | Agency Mortgage Backed Securities | Freddie Mac
Collateral Positions
Fair Value/ Carrying Value	54,959,000
Amortized Cost	55,898,000
Accrued Interest on Pledged MBS	129,000
Derivative contracts | Agency Mortgage Backed Securities | Ginnie Mae
Collateral Positions
Fair Value/ Carrying Value	6,267,000
Amortized Cost	6,144,000
Accrued Interest on Pledged MBS	$ 9,000

[1] Includes $1.276 billion of Non-Agency MBS acquired in connection with resecuritization transactions from consolidated VIEs at September 30, 2014, that are eliminated from the Company’s consolidated balance sheets.

[2] In addition, $736.8 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 September 30, 2014