Valuation (Schedule Of Financial Instruments) (Details) (USD $)	9 Months Ended		12 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	$ 56,366,000	[1]	$ 59,664,000	[1]
Fair value repurchase agreements	47,039,000	[1]	27,962,000	[1]
Investments sold short, at fair value-	(1,221,894,000)		(845,614,000)
Financial derivatives–liabilities, at fair value-	(47,331,000)	[1]	(44,791,000)	[1]
Securitized Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Security Owned and Pledged as Collateral, Fair Value	2,300,000		2,300,000
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	129,124,000		183,489,000
Total investments and financial derivatives–assets, at fair value and repurchase agreements	549,000		0
Total investments sold short, financial derivatives–liabilities, and securitized debt, at fair value	(19,417,000)		(8,742,000)
Level 1 [Member] | Investments Sold Short [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	(19,356,000)		(6,369,000)
Level 1 [Member] | Investments Sold Short [Member] | Agency residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	0		0
Level 1 [Member] | Investments Sold Short [Member] | Government debt sold short [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	0		0
Level 1 [Member] | Investments Sold Short [Member] | Common Stock Sold Short [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	(19,356,000)		(6,369,000)
Level 1 [Member] | Financial Derivatives - Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(61,000)		(2,373,000)
Level 1 [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Asset Backed Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 1 [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Asset Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 1 [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Corporate Bond Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 1 [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0
Level 1 [Member] | Financial Derivatives - Liabilities [Member] | Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 1 [Member] | Financial Derivatives - Liabilities [Member] | Total Return Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 1 [Member] | Financial Derivatives - Liabilities [Member] | Swaption [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0
Level 1 [Member] | Financial Derivatives - Liabilities [Member] | Put Option [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 1 [Member] | Financial Derivatives - Liabilities [Member] | Futures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(61,000)		(2,373,000)
Level 1 [Member] | Financial Derivatives - Liabilities [Member] | Forwards [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 1 [Member] | Securitized Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securitized debt(1)	0	[2]	0	[3]
Level 1 [Member] | Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0		0
Level 1 [Member] | Investments [Member] | Agency residential mortgage-backed securities and U.S. Treasury securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0
Level 1 [Member] | Investments [Member] | Agency residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-			0
Level 1 [Member] | Investments [Member] | Private Label Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0		0
Level 1 [Member] | Investments [Member] | Private Label Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0		0
Level 1 [Member] | Investments [Member] | Commercial Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0		0
Level 1 [Member] | Investments [Member] | Residential Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0		0
Level 1 [Member] | Investments [Member] | Other Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-			0
Level 1 [Member] | Investments [Member] | Other sset-backed securities and loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0
Level 1 [Member] | Investments [Member] | Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0
Level 1 [Member] | Investments [Member] | Private Corporate Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0
Level 1 [Member] | Financial Derivatives - Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	549,000		0
Level 1 [Member] | Financial Derivatives - Assets [Member] | Credit Default Swaps On Asset Backed Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0		0
Level 1 [Member] | Financial Derivatives - Assets [Member] | Credit Default Swaps On Asset Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0		0
Level 1 [Member] | Financial Derivatives - Assets [Member] | Credit Default Swaps On Corporate Bond Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0		0
Level 1 [Member] | Financial Derivatives - Assets [Member] | Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0		0
Level 1 [Member] | Financial Derivatives - Assets [Member] | Total Return Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0		0
Level 1 [Member] | Financial Derivatives - Assets [Member] | Swaption [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0
Level 1 [Member] | Financial Derivatives - Assets [Member] | Put Option [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0		0
Level 1 [Member] | Financial Derivatives - Assets [Member] | Futures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	549,000
Level 1 [Member] | Financial Derivatives - Assets [Member] | Forwards [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0
Level 1 [Member] | Repurchase Agreements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value repurchase agreements	0		0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0		0
Total investments and financial derivatives–assets, at fair value and repurchase agreements	1,772,636,000		1,060,822,000
Total investments sold short, financial derivatives–liabilities, and securitized debt, at fair value	(1,249,430,000)		(881,313,000)
Level 2 [Member] | Investments Sold Short [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	(1,202,538,000)		(839,245,000)
Level 2 [Member] | Investments Sold Short [Member] | Agency residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	(1,158,892,000)		(811,957,000)
Level 2 [Member] | Investments Sold Short [Member] | Government debt sold short [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	(43,646,000)		(27,288,000)
Level 2 [Member] | Investments Sold Short [Member] | Common Stock Sold Short [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	0		0
Level 2 [Member] | Financial Derivatives - Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(46,892,000)		(42,068,000)
Level 2 [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Asset Backed Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(4,385,000)		(11,866,000)
Level 2 [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Asset Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 2 [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Corporate Bond Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(23,629,000)		(24,949,000)
Level 2 [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(2,695,000)
Level 2 [Member] | Financial Derivatives - Liabilities [Member] | Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(15,766,000)		(5,064,000)
Level 2 [Member] | Financial Derivatives - Liabilities [Member] | Total Return Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(40,000)		(67,000)
Level 2 [Member] | Financial Derivatives - Liabilities [Member] | Swaption [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(213,000)
Level 2 [Member] | Financial Derivatives - Liabilities [Member] | Put Option [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(164,000)		(84,000)
Level 2 [Member] | Financial Derivatives - Liabilities [Member] | Futures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 2 [Member] | Financial Derivatives - Liabilities [Member] | Forwards [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		(38,000)
Level 2 [Member] | Securitized Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securitized debt(1)	0	[2]	0	[3]
Level 2 [Member] | Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	1,682,568,000		989,842,000
Level 2 [Member] | Investments [Member] | Agency residential mortgage-backed securities and U.S. Treasury securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	1,682,568,000
Level 2 [Member] | Investments [Member] | Agency residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-			989,842,000
Level 2 [Member] | Investments [Member] | Private Label Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0		0
Level 2 [Member] | Investments [Member] | Private Label Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0		0
Level 2 [Member] | Investments [Member] | Commercial Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0		0
Level 2 [Member] | Investments [Member] | Residential Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0		0
Level 2 [Member] | Investments [Member] | Other Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-			0
Level 2 [Member] | Investments [Member] | Other sset-backed securities and loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0
Level 2 [Member] | Investments [Member] | Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0
Level 2 [Member] | Investments [Member] | Private Corporate Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	0
Level 2 [Member] | Financial Derivatives - Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	43,029,000		43,018,000
Level 2 [Member] | Financial Derivatives - Assets [Member] | Credit Default Swaps On Asset Backed Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	2,304,000		4,937,000
Level 2 [Member] | Financial Derivatives - Assets [Member] | Credit Default Swaps On Asset Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0		0
Level 2 [Member] | Financial Derivatives - Assets [Member] | Credit Default Swaps On Corporate Bond Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	20,044,000		14,273,000
Level 2 [Member] | Financial Derivatives - Assets [Member] | Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	19,964,000		23,553,000
Level 2 [Member] | Financial Derivatives - Assets [Member] | Total Return Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	29,000		4,000
Level 2 [Member] | Financial Derivatives - Assets [Member] | Swaption [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	261,000
Level 2 [Member] | Financial Derivatives - Assets [Member] | Put Option [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	31,000		251,000
Level 2 [Member] | Financial Derivatives - Assets [Member] | Futures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0
Level 2 [Member] | Financial Derivatives - Assets [Member] | Forwards [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	396,000
Level 2 [Member] | Repurchase Agreements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value repurchase agreements	47,039,000		27,962,000
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0		0
Total investments and financial derivatives–assets, at fair value and repurchase agreements	771,048,000		756,934,000
Total investments sold short, financial derivatives–liabilities, and securitized debt, at fair value	(1,248,000)		(1,333,000)
Level 3 [Member] | Investments Sold Short [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	0		0
Level 3 [Member] | Investments Sold Short [Member] | Agency residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	0		0
Level 3 [Member] | Investments Sold Short [Member] | Government debt sold short [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	0		0
Level 3 [Member] | Investments Sold Short [Member] | Common Stock Sold Short [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	0		0
Level 3 [Member] | Financial Derivatives - Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(378,000)		(350,000)
Level 3 [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Asset Backed Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 3 [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Asset Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(378,000)		(350,000)
Level 3 [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Corporate Bond Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 3 [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0
Level 3 [Member] | Financial Derivatives - Liabilities [Member] | Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 3 [Member] | Financial Derivatives - Liabilities [Member] | Total Return Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 3 [Member] | Financial Derivatives - Liabilities [Member] | Swaption [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0
Level 3 [Member] | Financial Derivatives - Liabilities [Member] | Put Option [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 3 [Member] | Financial Derivatives - Liabilities [Member] | Futures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 3 [Member] | Financial Derivatives - Liabilities [Member] | Forwards [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		0
Level 3 [Member] | Securitized Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securitized debt(1)	(870,000)	[2]	(983,000)	[3]
Level 3 [Member] | Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	758,260,000		740,288,000
Level 3 [Member] | Investments [Member] | Agency residential mortgage-backed securities and U.S. Treasury securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	38,572,000
Level 3 [Member] | Investments [Member] | Agency residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-			40,504,000
Level 3 [Member] | Investments [Member] | Private Label Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	502,070,000		580,772,000
Level 3 [Member] | Investments [Member] | Private Label Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	46,317,000		32,994,000
Level 3 [Member] | Investments [Member] | Commercial Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	29,852,000		23,887,000
Level 3 [Member] | Investments [Member] | Residential Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	17,147,000		24,062,000
Level 3 [Member] | Investments [Member] | Other Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-			38,069,000
Level 3 [Member] | Investments [Member] | Other sset-backed securities and loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	109,152,000
Level 3 [Member] | Investments [Member] | Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	7,464,000
Level 3 [Member] | Investments [Member] | Private Corporate Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	7,686,000
Level 3 [Member] | Financial Derivatives - Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	12,788,000		16,646,000
Level 3 [Member] | Financial Derivatives - Assets [Member] | Credit Default Swaps On Asset Backed Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0		0
Level 3 [Member] | Financial Derivatives - Assets [Member] | Credit Default Swaps On Asset Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	12,788,000		16,646,000
Level 3 [Member] | Financial Derivatives - Assets [Member] | Credit Default Swaps On Corporate Bond Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0		0
Level 3 [Member] | Financial Derivatives - Assets [Member] | Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0		0
Level 3 [Member] | Financial Derivatives - Assets [Member] | Total Return Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0		0
Level 3 [Member] | Financial Derivatives - Assets [Member] | Swaption [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0
Level 3 [Member] | Financial Derivatives - Assets [Member] | Put Option [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0		0
Level 3 [Member] | Financial Derivatives - Assets [Member] | Futures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0
Level 3 [Member] | Financial Derivatives - Assets [Member] | Forwards [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	0
Level 3 [Member] | Repurchase Agreements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value repurchase agreements	0		0
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	129,124,000		183,489,000
Total investments and financial derivatives–assets, at fair value and repurchase agreements	2,544,233,000		1,817,756,000
Total investments sold short, financial derivatives–liabilities, and securitized debt, at fair value	(1,270,095,000)		(891,388,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments Sold Short [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	(1,221,894,000)		(845,614,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments Sold Short [Member] | Agency residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	(1,158,892,000)		(811,957,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments Sold Short [Member] | Government debt sold short [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	(43,646,000)		(27,288,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments Sold Short [Member] | Common Stock Sold Short [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments sold short, at fair value-	(19,356,000)		(6,369,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(47,331,000)		(44,791,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Asset Backed Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(4,385,000)		(11,866,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Asset Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(378,000)		(350,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Corporate Bond Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(23,629,000)		(24,949,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(2,695,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Liabilities [Member] | Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(15,766,000)		(5,064,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Liabilities [Member] | Total Return Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(40,000)		(67,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Liabilities [Member] | Swaption [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(213,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Liabilities [Member] | Put Option [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(164,000)		(84,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Liabilities [Member] | Futures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	(61,000)		(2,373,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Liabilities [Member] | Forwards [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–liabilities, at fair value-	0		(38,000)
Estimate of Fair Value, Fair Value Disclosure [Member] | Securitized Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securitized debt(1)	(870,000)	[2]	(983,000)	[3]
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	2,440,828,000		1,730,130,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments [Member] | Agency residential mortgage-backed securities and U.S. Treasury securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	1,721,140,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments [Member] | Agency residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-			1,030,346,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments [Member] | Private Label Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	502,070,000		580,772,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments [Member] | Private Label Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	46,317,000		32,994,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments [Member] | Commercial Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	29,852,000		23,887,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments [Member] | Residential Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	17,147,000		24,062,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments [Member] | Other Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-			38,069,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments [Member] | Other sset-backed securities and loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	109,152,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments [Member] | Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	7,464,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Investments [Member] | Private Corporate Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, at fair value-	7,686,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	56,366,000		59,664,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Assets [Member] | Credit Default Swaps On Asset Backed Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	2,304,000		4,937,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Assets [Member] | Credit Default Swaps On Asset Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	12,788,000		16,646,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Assets [Member] | Credit Default Swaps On Corporate Bond Indices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	20,044,000		14,273,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Assets [Member] | Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	19,964,000		23,553,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Assets [Member] | Total Return Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	29,000		4,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Assets [Member] | Swaption [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	261,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Assets [Member] | Put Option [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	31,000		251,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Assets [Member] | Futures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	549,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Financial Derivatives - Assets [Member] | Forwards [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial derivatives–assets, at fair value-	396,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Repurchase Agreements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value repurchase agreements	47,039,000		27,962,000
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Level 1 To Level 2 To Level 3 Transfers Amount	$ 0		$ 0

[1] In the Company's Consolidated Statement of Assets, Liabilities, and Equity, all balances associated with repurchase agreements, reverse repurchase agreements, and financial derivatives are presented on a gross basis.

[2] The asset subject to the resecuritization had a fair value of $2.3 million as of September 30, 2014, which is included on the Consolidated Schedule of Investments under Principal and Interest Private – Label Securities.

[3] The asset subject to the resecuritization had a fair value of $2.3 million as of December 31, 2013, which is included on the Consolidated Schedule of Investments under Principal and Interest Private – Label Securities.