Consolidated Condensed Schedule Of Investments (Investments Sold Short) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Investments Sold, Not yet Purchased [Line Items]
Investments sold short at fair value-	$ (622,301)		$ (462,394)
Proceeds from investments sold short	(621,048)		(459,013)
TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Investments sold short at fair value-	(608,720)	[1],[2]	(446,707)	[1],[3]
Proceeds from investments sold short	(607,967)	[1],[2]	(443,893)	[1],[3]
Investments sold not yet purchased as a percentage of net assets	(120.22%)	[1],[2]	(120.43%)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association [Member]
Investments Sold, Not yet Purchased [Line Items]
Investments sold not yet purchased as a percentage of net assets	(105.27%)		(93.03%)
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 3.50% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(198,168)	[1],[2]
Description	Federal National Mortgage Association (30 Year)	[1],[2]
Rate	3.50%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(211,343)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 5.00% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(87,500)	[1],[2]
Description	Federal National Mortgage Association (30 Year)	[1],[2]
Rate	5.00%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(94,794)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 4.50% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(77,730)	[1],[2]
Description	Federal National Mortgage Association (30 Year)	[1],[2]
Rate	4.50%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(83,982)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal Home Loan Mortgage Corporation (30 Year) 3.50% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(53,400)	[1],[2]
Description	Federal Home Loan Mortgage Corporation (30 Year)	[1],[2]
Rate	3.50%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(56,804)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (15 Year) 3.00% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(34,510)	[1],[2]
Description	Federal National Mortgage Association (15 Year)	[1],[2]
Rate	3.00%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(36,430)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 3.00% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(31,600)	[1],[2]
Description	Federal National Mortgage Association (30 Year)	[1],[2]
Rate	3.00%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(33,128)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal Home Loan Mortgage Corporation (30 Year) 5.00% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(16,500)	[1],[2]
Description	Federal Home Loan Mortgage Corporation (30 Year)	[1],[2]
Rate	5.00%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(17,776)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (15 Year) 3.50% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(16,450)	[1],[2]
Description	Federal National Mortgage Association (15 Year)	[1],[2]
Rate	3.50%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(17,460)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 4.00% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(15,718)	[1],[2]
Description	Federal National Mortgage Association (30 Year)	[1],[2]
Rate	4.00%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(16,852)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (15 Year) 4.00% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(14,104)	[1],[2]
Description	Federal National Mortgage Association (15 Year)	[1],[2]
Rate	4.00%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(15,096)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (15 Year) 4.50% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(11,000)	[1],[2]
Description	Federal National Mortgage Association (15 Year)	[1],[2]
Rate	4.50%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(11,833)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 5.50% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(7,500)	[1],[2]
Description	Federal National Mortgage Association (30 Year)	[1],[2]
Rate	5.50%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(8,148)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 6.00% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(2,500)	[1],[2]
Description	Federal National Mortgage Association (30 Year)	[1],[2]
Rate	6.00%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(2,731)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Other Federal National Mortgage Association (15 Year) 2.50% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(1,200)	[1],[2]
Description	Other Federal National Mortgage Association (15 Year)	[1],[2]
Rate	2.50%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(1,255)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Other Federal Home Loan Mortgage Corporation (30 Year) 6.00% 2013-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(1,000)	[1],[2]
Description	Other Federal Home Loan Mortgage Corporation (30 Year)	[1],[2]
Rate	6.00%	[1],[2]
Investments maturity date	2013-01	[1],[2]
Investments sold short at fair value-	(1,088)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 4.50% 2012-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount			(147,700)	[1],[3]
Description			Federal National Mortgage Association (30 Year)	[1],[3]
Rate			4.50%	[1],[3]
Investments maturity date			2012-01	[1],[3]
Investments sold short at fair value-			(157,185)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 5.00% 2012-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount			(114,200)	[1],[3]
Description			Federal National Mortgage Association (30 Year)	[1],[3]
Rate			5.00%	[1],[3]
Investments maturity date			2012-01	[1],[3]
Investments sold short at fair value-			(123,376)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal Home Loan Mortgage Corporation (30 Year) 5.00% 2012-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount			(31,000)	[1],[3]
Description			Federal Home Loan Mortgage Corporation (30 Year)	[1],[3]
Rate			5.00%	[1],[3]
Investments maturity date			2012-01	[1],[3]
Investments sold short at fair value-			(33,316)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal Home Loan Mortgage Corporation (30 Year) 4.50% 2012-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount			(30,400)	[1],[3]
Description			Federal Home Loan Mortgage Corporation (30 Year)	[1],[3]
Rate			4.50%	[1],[3]
Investments maturity date			2012-01	[1],[3]
Investments sold short at fair value-			(32,217)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Government National Mortgage Association (30 Year) 5.00% 2012-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount			(26,000)	[1],[3]
Description			Government National Mortgage Association (30 Year)	[1],[3]
Rate			5.00%	[1],[3]
Investments maturity date			2012-01	[1],[3]
Investments sold short at fair value-			(28,805)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (15 Year) 4.00% 2012-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount			(25,300)	[1],[3]
Description			Federal National Mortgage Association (15 Year)	[1],[3]
Rate			4.00%	[1],[3]
Investments maturity date			2012-01	[1],[3]
Investments sold short at fair value-			(26,688)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 5.50% 2012-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount			(13,500)	[1],[3]
Description			Federal National Mortgage Association (30 Year)	[1],[3]
Rate			5.50%	[1],[3]
Investments maturity date			2012-01	[1],[3]
Investments sold short at fair value-			(14,700)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (15 Year) 4.50% 2012-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount			(11,000)	[1],[3]
Description			Federal National Mortgage Association (15 Year)	[1],[3]
Rate			4.50%	[1],[3]
Investments maturity date			2012-01	[1],[3]
Investments sold short at fair value-			(11,727)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 3.50% 2012-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount			(8,400)	[1],[3]
Description			Federal National Mortgage Association (30 Year)	[1],[3]
Rate			3.50%	[1],[3]
Investments maturity date			2012-01	[1],[3]
Investments sold short at fair value-			(8,640)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal Home Loan Mortgage Corporation (30 Year) 3.50% 2012-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount			(4,400)	[1],[3]
Description			Federal Home Loan Mortgage Corporation (30 Year)	[1],[3]
Rate			3.50%	[1],[3]
Investments maturity date			2012-01	[1],[3]
Investments sold short at fair value-			(4,517)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 6.00% 2012-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount			(2,500)	[1],[3]
Description			Federal National Mortgage Association (30 Year)	[1],[3]
Rate			6.00%	[1],[3]
Investments maturity date			2012-01	[1],[3]
Investments sold short at fair value-			(2,753)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Other Government National Mortgage Association (30 Year) 5.50% 2012-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount			(1,500)	[1],[3]
Description			Other Government National Mortgage Association (30 Year)	[1],[3]
Rate			5.50%	[1],[3]
Investments maturity date			2012-01	[1],[3]
Investments sold short at fair value-			(1,685)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Other Federal Home Loan Mortgage Corporation (30 Year) 6.00% 2012-01 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount			(1,000)	[1],[3]
Description			Other Federal Home Loan Mortgage Corporation (30 Year)	[1],[3]
Rate			6.00%	[1],[3]
Investments maturity date			2012-01	[1],[3]
Investments sold short at fair value-			(1,098)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal Home Loan Mortgage Corporation [Member]
Investments Sold, Not yet Purchased [Line Items]
Investments sold not yet purchased as a percentage of net assets	(14.95%)		(19.18%)
TBA - Fixed Rate Agency Securities Sold Short [Member] | Government National Mortgage Association [Member]
Investments Sold, Not yet Purchased [Line Items]
Investments sold not yet purchased as a percentage of net assets			(8.22%)
U.S. Treasury Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Investments sold short at fair value-	(13,581)	[1]	(15,687)	[1]
Proceeds from investments sold short	(13,081)	[1]	(15,120)	[1]
Investments sold not yet purchased as a percentage of net assets	(2.68%)	[1]	(4.23%)	[1]
U.S. Treasury Securities Sold Short [Member] | U.S. Treasury Note 1.75% 2016-05 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(13,000)	[1]	(15,000)	[1]
Description	U.S. Treasury Note	[1]	U.S. Treasury Note	[1]
Rate	1.75%	[1]	1.75%	[1]
Investments maturity date	2016-05	[1]	2016-05	[1]
Investments sold short at fair value-	(13,581)	[1]	(15,687)	[1]
Securities Sold Short - Securities Sold, Not Yet Purchased [Member]
Investments Sold, Not yet Purchased [Line Items]
Investments sold short at fair value-	(622,301)	[1]	(462,394)	[1]
Proceeds from investments sold short	$ (621,048)	[1]	$ (459,013)	[1]
Investments sold not yet purchased as a percentage of net assets	(122.90%)	[1]	(124.66%)	[1]

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

[2] 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.

[3] 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.