Valuation (Schedule Of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified																																																																																																																																																																													3 Months Ended
	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2013 Level 1 [Member]	Dec. 31, 2012 Level 1 [Member]	Mar. 31, 2013 Level 1 [Member] Investments Sold Short [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Dec. 31, 2012 Level 1 [Member] Investments Sold Short [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Mar. 31, 2013 Level 1 [Member] Financial Derivatives - Liabilities [Member]	Dec. 31, 2012 Level 1 [Member] Financial Derivatives - Liabilities [Member]	Mar. 31, 2013 Level 1 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Corporate Indices [Member]	Dec. 31, 2012 Level 1 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Corporate Indices [Member]	Mar. 31, 2013 Level 1 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Indices [Member]	Dec. 31, 2012 Level 1 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Indices [Member]	Mar. 31, 2013 Level 1 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Securities [Member]	Dec. 31, 2012 Level 1 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Securities [Member]	Mar. 31, 2013 Level 1 [Member] Financial Derivatives - Liabilities [Member] Interest Rate Swaps [Member]	Dec. 31, 2012 Level 1 [Member] Financial Derivatives - Liabilities [Member] Interest Rate Swaps [Member]	Mar. 31, 2013 Level 1 [Member] Financial Derivatives - Liabilities [Member] Total Return Swaps [Member]	Dec. 31, 2012 Level 1 [Member] Financial Derivatives - Liabilities [Member] Total Return Swaps [Member]	Mar. 31, 2013 Level 1 [Member] Financial Derivatives - Liabilities [Member] Unrealized Depreciation On Future Contracts [Member]	Dec. 31, 2012 Level 1 [Member] Financial Derivatives - Liabilities [Member] Unrealized Depreciation On Future Contracts [Member]	Mar. 31, 2013 Level 1 [Member] Securitized Debt [Member]	Dec. 31, 2012 Level 1 [Member] Securitized Debt [Member]	Mar. 31, 2013 Level 1 [Member] Investments [Member]	Dec. 31, 2012 Level 1 [Member] Investments [Member]	Mar. 31, 2013 Level 1 [Member] Investments [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Dec. 31, 2012 Level 1 [Member] Investments [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Mar. 31, 2013 Level 1 [Member] Investments [Member] Private Label Residential Mortgage-Backed Securities [Member]	Dec. 31, 2012 Level 1 [Member] Investments [Member] Private Label Residential Mortgage-Backed Securities [Member]	Mar. 31, 2013 Level 1 [Member] Investments [Member] Private Label Commercial Mortgage-Backed Securities [Member]	Dec. 31, 2012 Level 1 [Member] Investments [Member] Private Label Commercial Mortgage-Backed Securities [Member]	Mar. 31, 2013 Level 1 [Member] Investments [Member] Commercial Mortgage Loans [Member]	Dec. 31, 2012 Level 1 [Member] Investments [Member] Commercial Mortgage Loans [Member]	Mar. 31, 2013 Level 1 [Member] Investments [Member] Asset-backed Securities [Member]	Mar. 31, 2013 Level 1 [Member] Financial Derivatives - Assets [Member]	Dec. 31, 2012 Level 1 [Member] Financial Derivatives - Assets [Member]	Mar. 31, 2013 Level 1 [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Indices [Member]	Dec. 31, 2012 Level 1 [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Indices [Member]	Mar. 31, 2013 Level 1 [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Securities [Member]	Dec. 31, 2012 Level 1 [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Securities [Member]	Mar. 31, 2013 Level 1 [Member] Financial Derivatives - Assets [Member] Interest Rate Swaps [Member]	Dec. 31, 2012 Level 1 [Member] Financial Derivatives - Assets [Member] Interest Rate Swaps [Member]	Mar. 31, 2013 Level 1 [Member] Financial Derivatives - Assets [Member] Total Return Swaps [Member]	Mar. 31, 2013 Level 1 [Member] Repurchase Agreements [Member]	Dec. 31, 2012 Level 1 [Member] Repurchase Agreements [Member]	Mar. 31, 2013 Level 2 [Member]	Dec. 31, 2012 Level 2 [Member]	Mar. 31, 2013 Level 2 [Member] Investments Sold Short [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Dec. 31, 2012 Level 2 [Member] Investments Sold Short [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Mar. 31, 2013 Level 2 [Member] Financial Derivatives - Liabilities [Member]	Dec. 31, 2012 Level 2 [Member] Financial Derivatives - Liabilities [Member]	Mar. 31, 2013 Level 2 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Corporate Indices [Member]	Dec. 31, 2012 Level 2 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Corporate Indices [Member]	Mar. 31, 2013 Level 2 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Indices [Member]	Dec. 31, 2012 Level 2 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Indices [Member]	Mar. 31, 2013 Level 2 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Securities [Member]	Dec. 31, 2012 Level 2 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Securities [Member]	Mar. 31, 2013 Level 2 [Member] Financial Derivatives - Liabilities [Member] Interest Rate Swaps [Member]	Dec. 31, 2012 Level 2 [Member] Financial Derivatives - Liabilities [Member] Interest Rate Swaps [Member]	Mar. 31, 2013 Level 2 [Member] Financial Derivatives - Liabilities [Member] Total Return Swaps [Member]	Dec. 31, 2012 Level 2 [Member] Financial Derivatives - Liabilities [Member] Total Return Swaps [Member]	Mar. 31, 2013 Level 2 [Member] Financial Derivatives - Liabilities [Member] Unrealized Depreciation On Future Contracts [Member]	Dec. 31, 2012 Level 2 [Member] Financial Derivatives - Liabilities [Member] Unrealized Depreciation On Future Contracts [Member]	Mar. 31, 2013 Level 2 [Member] Securitized Debt [Member]	Dec. 31, 2012 Level 2 [Member] Securitized Debt [Member]	Mar. 31, 2013 Level 2 [Member] Investments [Member]	Dec. 31, 2012 Level 2 [Member] Investments [Member]	Mar. 31, 2013 Level 2 [Member] Investments [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Dec. 31, 2012 Level 2 [Member] Investments [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Mar. 31, 2013 Level 2 [Member] Investments [Member] Private Label Residential Mortgage-Backed Securities [Member]	Dec. 31, 2012 Level 2 [Member] Investments [Member] Private Label Residential Mortgage-Backed Securities [Member]	Mar. 31, 2013 Level 2 [Member] Investments [Member] Private Label Commercial Mortgage-Backed Securities [Member]	Dec. 31, 2012 Level 2 [Member] Investments [Member] Private Label Commercial Mortgage-Backed Securities [Member]	Mar. 31, 2013 Level 2 [Member] Investments [Member] Commercial Mortgage Loans [Member]	Dec. 31, 2012 Level 2 [Member] Investments [Member] Commercial Mortgage Loans [Member]	Mar. 31, 2013 Level 2 [Member] Investments [Member] Asset-backed Securities [Member]	Mar. 31, 2013 Level 2 [Member] Financial Derivatives - Assets [Member]	Dec. 31, 2012 Level 2 [Member] Financial Derivatives - Assets [Member]	Mar. 31, 2013 Level 2 [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Indices [Member]	Dec. 31, 2012 Level 2 [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Indices [Member]	Mar. 31, 2013 Level 2 [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Securities [Member]	Dec. 31, 2012 Level 2 [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Securities [Member]	Mar. 31, 2013 Level 2 [Member] Financial Derivatives - Assets [Member] Interest Rate Swaps [Member]	Dec. 31, 2012 Level 2 [Member] Financial Derivatives - Assets [Member] Interest Rate Swaps [Member]	Mar. 31, 2013 Level 2 [Member] Financial Derivatives - Assets [Member] Total Return Swaps [Member]	Mar. 31, 2013 Level 2 [Member] Repurchase Agreements [Member]	Dec. 31, 2012 Level 2 [Member] Repurchase Agreements [Member]	Mar. 31, 2013 Level 3 [Member]	Dec. 31, 2012 Level 3 [Member]	Mar. 31, 2013 Level 3 [Member] Investments Sold Short [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Dec. 31, 2012 Level 3 [Member] Investments Sold Short [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Mar. 31, 2013 Level 3 [Member] Financial Derivatives - Liabilities [Member]	Dec. 31, 2012 Level 3 [Member] Financial Derivatives - Liabilities [Member]	Mar. 31, 2013 Level 3 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Corporate Indices [Member]	Dec. 31, 2012 Level 3 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Corporate Indices [Member]	Mar. 31, 2013 Level 3 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Indices [Member]	Dec. 31, 2012 Level 3 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Indices [Member]	Mar. 31, 2013 Level 3 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Securities [Member]	Dec. 31, 2012 Level 3 [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Securities [Member]	Mar. 31, 2013 Level 3 [Member] Financial Derivatives - Liabilities [Member] Interest Rate Swaps [Member]	Dec. 31, 2012 Level 3 [Member] Financial Derivatives - Liabilities [Member] Interest Rate Swaps [Member]	Mar. 31, 2013 Level 3 [Member] Financial Derivatives - Liabilities [Member] Total Return Swaps [Member]	Dec. 31, 2012 Level 3 [Member] Financial Derivatives - Liabilities [Member] Total Return Swaps [Member]	Mar. 31, 2013 Level 3 [Member] Financial Derivatives - Liabilities [Member] Unrealized Depreciation On Future Contracts [Member]	Dec. 31, 2012 Level 3 [Member] Financial Derivatives - Liabilities [Member] Unrealized Depreciation On Future Contracts [Member]	Mar. 31, 2013 Level 3 [Member] Securitized Debt [Member]	Dec. 31, 2012 Level 3 [Member] Securitized Debt [Member]	Mar. 31, 2013 Level 3 [Member] Investments [Member]	Dec. 31, 2012 Level 3 [Member] Investments [Member]	Mar. 31, 2013 Level 3 [Member] Investments [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Dec. 31, 2012 Level 3 [Member] Investments [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Mar. 31, 2013 Level 3 [Member] Investments [Member] Private Label Residential Mortgage-Backed Securities [Member]	Dec. 31, 2012 Level 3 [Member] Investments [Member] Private Label Residential Mortgage-Backed Securities [Member]	Mar. 31, 2013 Level 3 [Member] Investments [Member] Private Label Commercial Mortgage-Backed Securities [Member]	Dec. 31, 2012 Level 3 [Member] Investments [Member] Private Label Commercial Mortgage-Backed Securities [Member]	Mar. 31, 2013 Level 3 [Member] Investments [Member] Commercial Mortgage Loans [Member]	Dec. 31, 2012 Level 3 [Member] Investments [Member] Commercial Mortgage Loans [Member]	Mar. 31, 2013 Level 3 [Member] Investments [Member] Asset-backed Securities [Member]	Mar. 31, 2013 Level 3 [Member] Financial Derivatives - Assets [Member]	Dec. 31, 2012 Level 3 [Member] Financial Derivatives - Assets [Member]	Mar. 31, 2013 Level 3 [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Indices [Member]	Dec. 31, 2012 Level 3 [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Indices [Member]	Mar. 31, 2013 Level 3 [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Securities [Member]	Dec. 31, 2012 Level 3 [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Securities [Member]	Mar. 31, 2013 Level 3 [Member] Financial Derivatives - Assets [Member] Interest Rate Swaps [Member]	Dec. 31, 2012 Level 3 [Member] Financial Derivatives - Assets [Member] Interest Rate Swaps [Member]	Mar. 31, 2013 Level 3 [Member] Financial Derivatives - Assets [Member] Total Return Swaps [Member]	Mar. 31, 2013 Level 3 [Member] Repurchase Agreements [Member]	Dec. 31, 2012 Level 3 [Member] Repurchase Agreements [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Investments Sold Short [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Investments Sold Short [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Liabilities [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Liabilities [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Corporate Indices [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Corporate Indices [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Indices [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Indices [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Securities [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Liabilities [Member] Credit Default Swaps On Asset Backed Securities [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Liabilities [Member] Interest Rate Swaps [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Liabilities [Member] Interest Rate Swaps [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Liabilities [Member] Total Return Swaps [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Liabilities [Member] Total Return Swaps [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Liabilities [Member] Unrealized Depreciation On Future Contracts [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Liabilities [Member] Unrealized Depreciation On Future Contracts [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Securitized Debt [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Securitized Debt [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Investments [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Investments [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Investments [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Investments [Member] U.S. Treasury And Agency Residential Mortgage-Backed Securities [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Investments [Member] Private Label Residential Mortgage-Backed Securities [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Investments [Member] Private Label Residential Mortgage-Backed Securities [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Investments [Member] Private Label Commercial Mortgage-Backed Securities [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Investments [Member] Private Label Commercial Mortgage-Backed Securities [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Investments [Member] Commercial Mortgage Loans [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Investments [Member] Commercial Mortgage Loans [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Investments [Member] Asset-backed Securities [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Assets [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Assets [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Indices [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Indices [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Securities [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Assets [Member] Credit Default Swaps On Asset Backed Securities [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Assets [Member] Interest Rate Swaps [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Assets [Member] Interest Rate Swaps [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Financial Derivatives - Assets [Member] Total Return Swaps [Member]	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Repurchase Agreements [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Repurchase Agreements [Member]	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member]	Mar. 31, 2012 Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents					$ 64,753	$ 59,084																																									$ 0	$ 0																																									$ 0	$ 0																																									$ 64,753	$ 59,084
Investments at fair value-																									0	0	0	0	0	0	0	0	0	0	0																																934,747	811,233	934,747	811,233	0	0	0	0	0	0	0																																601,177	563,883	16,228	6,644	557,820	528,366	5,778	19,327	9,713	9,546	11,638																																1,535,924	1,375,116	950,975	817,877	557,820	528,366	5,778	19,327	9,713	9,546	11,638
Financial derivatives-assets at fair value-	36,250		48,504																																	0	0	0	0	0	0	0	0	0																																		9,852	12,473	9,407	12,468	0	0	384	5	61																																		26,398	36,031	0	0	26,398	36,031	0	0	0																																		36,250	48,504	9,407	12,468	26,398	36,031	384	5	61
Fair value	42,614	[1]	13,650	[1]																																									0	0																																									42,614	13,650																																									0	0																																									42,614	13,650
Total investments, financial derivatives-assets at fair value, and repurchase agreements					0	0																																									987,213	837,356																																									627,575	599,914																																									1,614,788	1,437,270
Investments sold short at fair value-	(649,756)		(622,301)				0	0																																									(649,756)	(622,301)																																									0	0																																									(649,756)	(622,301)
Financial derivatives-liabilities at fair value-	(18,490)		(15,212)						(48)	(70)	0	0	0	0	0	0	0	0	0	0	(48)	(70)																													(18,440)	(15,141)	(2,759)	(484)	(14,170)	(13,468)	0	0	(1,484)	(1,124)	(27)	(65)	0	0																													(2)	(1)	0	0	0	0	(2)	(1)	0	0	0	0	0	0																													(18,490)	(15,212)	(2,759)	(484)	(14,170)	(13,468)	(2)	(1)	(1,484)	(1,124)	(27)	(65)	(48)	(70)
Securitized debt																							0	0																																									0	0																																									(1,205)	(1,335)																																									(1,205)	(1,335)
Total investments sold short, financial derivatives-liabilities at fair value, and securitized debt					(48)	(70)																																									(668,196)	(637,442)																																									(1,207)	(1,336)																																									(669,451)	(638,848)
Transfers of financial instruments between Level 1, Level 2, or Level 3																																																																																																																																																																													$ 0	$ 0

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