Non Agency MBS (Details) (Mortgage-backed Securities, Issued by Private Enterprises [Member], USD $)	9 Months Ended
	Sep. 30, 2012		Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Principal/par value	$ 467,982,000		$ 376,972,000
Unamortized premium	95,822,000		54,885,000
Unamortized discount	(21,544,000)		(18,514,000)
Amortized cost	542,260,000		413,343,000
Available for sale securities, gross unrealized gains	46,294,000		13,206,000
Available for sale securities, gross unrealized losses	(1,623,000)		(5,453,000)
Total MBS investments at fair value	586,931,000		421,096,000
RMBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Principal/par value	15,007,000		17,119,000
Unamortized premium	0		0
Unamortized discount	(812,000)		(1,003,000)
Amortized cost	14,195,000		16,116,000
Available for sale securities, gross unrealized gains	470,000		507,000
Available for sale securities, gross unrealized losses	(424,000)		(1,353,000)
Total MBS investments at fair value			15,270,000
Weighted average coupon, MBS	4.38%		4.41%
Payments to Acquire Mortgage Backed Securities (MBS)	7,500,000
CMBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Principal/par value	452,975,000		359,853,000
Unamortized premium	2,726,000		3,646,000
Unamortized discount	(20,732,000)		(17,511,000)
Amortized cost	434,969,000		345,988,000
Available for sale securities, gross unrealized gains	41,507,000		11,806,000
Available for sale securities, gross unrealized losses	(1,194,000)		(3,724,000)
Total MBS investments at fair value	475,282,000		354,070,000
Weighted average coupon, MBS	4.64%		5.91%
Payments to Acquire Mortgage Backed Securities (MBS)	120,697,000
CMBS - IO [Member]
Schedule of Available-for-sale Securities [Line Items]
Principal/par value	0	[1]	0	[2]
Unamortized premium	93,096,000	[1]	51,239,000	[2]
Unamortized discount	0	[1]	0	[2]
Amortized cost	93,096,000	[1]	51,239,000	[2]
Available for sale securities, gross unrealized gains	4,317,000	[1]	893,000	[2]
Available for sale securities, gross unrealized losses	(5,000)	[1]	(376,000)	[2]
Total MBS investments at fair value	97,408,000	[1]	51,756,000	[2]
Weighted average coupon, MBS	0.69%	[1]	1.24%	[2]
Payments to Acquire Mortgage Backed Securities (MBS)	48,812
Notional balance of non-Agency IO investments	2,252,064,000		906,202,000
Estimate of Fair Value, Fair Value Disclosure [Member] | RMBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Total MBS investments at fair value	$ 14,241,000

[1] The combined notional balance for the non-Agency CMBS IO securities is $2,252,064 as of September 30, 2012.

[2] The combined notional balance for the non-Agency CMBS IO securities is $906,202 as of December 31, 2011.