Significant Accounting Policies (Details) (USD $)			12 Months Ended	1 Months Ended									12 Months Ended
	Dec. 31, 2012 counterparties	Dec. 31, 2011 counterparties	Dec. 31, 2012 Long-Term Incentive Plan Units [Member] Non-Manager [Member]	Aug. 31, 2010 Long-Term Incentive Plan Units [Member] Non-Employees [Member]	Dec. 31, 2012 TBA - Fixed Rate Agency Securities [Member]		Dec. 31, 2011 TBA - Fixed Rate Agency Securities [Member]		Dec. 31, 2012 TBA - Fixed Rate Agency Securities Sold Short [Member]		Dec. 31, 2011 TBA - Fixed Rate Agency Securities Sold Short [Member]		Dec. 31, 2012 Maximum [Member]	Dec. 31, 2011 Maximum [Member]	Dec. 31, 2012 Minimum [Member]	Dec. 31, 2011 Minimum [Member]	Dec. 31, 2012 Weighted Average [Member]	Dec. 31, 2011 Weighted Average [Member]	Dec. 31, 2012 Interest Rate Swaps [Member]	Dec. 31, 2011 Interest Rate Swaps [Member]	Dec. 31, 2012 Total Return Swaps [Member]	Dec. 31, 2011 Total Return Swaps [Member]	Dec. 31, 2012 Credit Default Swaps [Member]	Dec. 31, 2011 Credit Default Swaps [Member]	Dec. 31, 2012 Futures [Member]	Dec. 31, 2011 Futures [Member]
Significant Accounting Policies [Line Items]
Percentage of average monthly notional amount																			92.00%	111.00%	87.00%	354.00%	78.00%	92.00%	57.00%	65.00%
Reverse repurchase agreements remaining terms													180 days	180 days	10 days	3 days	57 days	33 days
Reverse repurchase agreements interest rate													2.31%	2.56%	0.37%	0.08%	0.77%	0.82%
Percentage of open reserve repurchase agreements	67.00%	73.00%
Number of counterparties	2	4
Fair value of asset subject to resecuritization	$ 2,400,000
Fair Value	1,375,116,000	1,212,483,000			43,610,000	[1],[2],[3]	32,033,000	[1],[4],[5]
Receivable for securities sold	626,919,000	533,708,000			608,500,000		443,700,000
Investments sold short at fair value-	(622,301,000)	(462,394,000)							(608,720,000)	[1],[6]	(446,707,000)	[1],[7]
Payable for securities purchased	57,333,000	127,517,000							43,800,000		32,500,000
Net short position, TBA									$ (565,100,000)		$ (414,700,000)
Vesting period			1 year
LTIP vesting period				3 years

[1] See Note 2 and Note 3 in Notes to Consolidated Financial Statements.

[2] The table below shows the Company’s long investment ratings from Moody’s, Standard and Poor’s, or Fitch, as well as the Company’s long investments that were unrated but affiliated with Fannie Mae, Freddie Mac, or Ginnie Mae. Ratings tend to be a lagging credit indicator; as a result, the credit quality of the Company’s long investment holdings may be lower than the credit quality implied based on the ratings listed below. In situations where an investment has a split rating, the lowest provided rating is used. The ratings descriptions include ratings qualified with a “+,” “-,” “1,” “2,” or “3.”Rating DescriptionPercent ofShareholders’EquityUnrated but Agency-Guaranteed161.52%Aaa/AAA/AAA0.01%Aa/AA/AA0.26%A/A/A1.02%Baa/BBB/BBB3.70%Ba/BB/BB or below102.40%Unrated2.66%

[3] At December 31, 2012, the Company’s long investments guaranteed by the Federal National Mortgage Association, the Federal Home Loan Mortgage Corporation, and the Government National Mortgage Association represented 119.78%, 40.49%, and 1.25% of shareholders’ equity, respectively.

[4] The table below shows the ratings on the Company’s long investments from Moody’s, Standard and Poor’s, or Fitch, as well as the Company’s long investments that were unrated but affiliated with Fannie Mae, Freddie Mac, or Ginnie Mae. Ratings tend to be a lagging credit indicator; as a result, the credit quality of the Company’s long investment holdings may be lower than the credit quality implied based on the ratings listed below. In situations where an investment has a split rating, the lowest provided rating is used. The ratings descriptions include ratings qualified with a “+,” “-,” “1,” “2,” or “3.”Rating DescriptionPercent ofShareholders’EquityU.S. Treasury Securities2.72%Unrated but Agency-Guaranteed206.07%Aaa/AAA/AAA1.25%Aa/AA/AA1.88%A/A/A5.44%Baa/BBB/BBB3.46%Ba/BB/BB or below103.36%Unrated2.71%

[5] At December 31, 2011, the Company’s long investments guaranteed by the Federal National Mortgage Association, the Federal Home Loan Mortgage Corporation, and the Government National Mortgage Association represented 142.04%, 63.62%, and 0.41% of shareholders’ equity, respectively.

[6] At December 31, 2012, the Company’s short investments guaranteed by the Federal National Mortgage Association and the Federal Home Loan Mortgage Corporation represented 105.27% and 14.95% of shareholders’ equity, respectively.

[7] At December 31, 2011, the Company’s short investments guaranteed by the Federal National Mortgage Association, the Federal Home Loan Mortgage Corporation, and the Government National Mortgage Association represented 93.03%, 19.18%, and 8.22% of shareholders’ equity, respectively.