Residential Mortgage-Backed Securities (Details 2) (USD $)	1 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2013 item	Dec. 31, 2012
Residential Mortgage-Backed Securities
Estimated fair value		$ 4,186,750,000	$ 4,186,750,000	$ 5,212,581,000
Number of investments in unrealized position for more than one year			0
Other loss on Residential mortgage-backed securities	87,000	3,533,000	5,801,000
Residential Mortgage-Backed Securities
Residential Mortgage-Backed Securities
Principal balance		3,891,146,000	3,891,146,000	4,582,727,000
Amortized cost of IOs and IIOs		199,132,000	199,132,000	176,093,000
Carrying value of Agency Interest-Only Strips accounted for as derivatives		99,574,000	99,574,000	75,387,000
Unamortized premium		292,849,000	292,849,000	382,614,000
Unamortized Discount		(30,762,000)	(30,762,000)	(5,511,000)
Non-Accretable Discount		(68,071,000)	(68,071,000)	(12,659,000)
Gross unrealized gains		11,987,000	11,987,000	25,395,000
Gross unrealized losses		(209,105,000)	(209,105,000)	(11,465,000)
Estimated fair value		4,186,750,000	4,186,750,000	5,212,581,000
Agency RMBS
Residential Mortgage-Backed Securities
Fair value		3,800,000,000	3,800,000,000
Unrealized loss position		205,700,000	205,700,000
Non-Agency RMBS
Residential Mortgage-Backed Securities
Principal balance		272,681,000	272,681,000	37,372,000
Non-Accretable Discount		(68,071,000)	(68,071,000)	(12,659,000)
Estimated fair value		173,574,000	173,574,000	19,073,000
Fair value		99,400,000	99,400,000
Unrealized loss position		$ 3,400,000	$ 3,400,000