Consolidated Condensed Schedule Of Investments (Investments Sold Short) (USD $) In Thousands, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2012		Dec. 31, 2011
Investments Sold, Not yet Purchased [Line Items]
Fair value	$ (494,524)		$ (462,394)
Proceeds from investments sold short	(493,130)		(459,013)
Securities Sold Short - Securities Sold, Not Yet Purchased [Member]
Investments Sold, Not yet Purchased [Line Items]
Fair value	(494,524)	[1]	(462,394)	[1]
Proceeds from investments sold short	(493,130)	[1]	(459,013)	[1]
Investments sold not yet purchased as a percentage of net assets	(125.11%)	[1]	(124.66%)	[1]
U.S. Treasury Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Fair value	(36,496)	[1]	(15,687)	[1]
Proceeds from investments sold short	(36,015)	[1]	(15,120)	[1]
Investments sold not yet purchased as a percentage of net assets	(9.23%)	[1]	(4.23%)	[1]
U.S. Treasury Securities Sold Short [Member] | U.S. Treasury Note 0.25% 2015-05 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(15,000)	[1]
Description	U.S. Treasury Note	[1]
Rate	0.25%	[1]
Investments maturity date	2015-05	[1]
Fair value	(14,936)	[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]
Fair value	(13,595)	[1]	(15,687)	[1]
U.S. Treasury Securities Sold Short [Member] | U.S. Treasury Note 0.63% 2017-05 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(8,000)	[1]
Description	U.S. Treasury Note	[1]
Rate	0.63%	[1]
Investments maturity date	2017-05	[1]
Fair value	(7,965)	[1]
TBA - Fixed Rate Agency Securities Sold Short [Member]
Investments Sold, Not yet Purchased [Line Items]
Fair value	(458,028)	[1],[2]	(446,707)	[1],[3]
Proceeds from investments sold short	(457,115)	[1],[2]	(443,893)	[1],[3]
Investments sold not yet purchased as a percentage of net assets	(115.88%)	[1],[2]	(120.43%)	[1],[3]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 4.00% 2012-07 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(224,970)	[1],[2]
Description	Federal National Mortgage Association (30 Year)	[1],[2]
Rate	4.00%	[1],[2]
Investments maturity date	2012-07	[1],[2]
Fair value	(239,461)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 4.50% 2012-07 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(73,330)	[1],[2]
Description	Federal National Mortgage Association (30 Year)	[1],[2]
Rate	4.50%	[1],[2]
Investments maturity date	2012-07	[1],[2]
Fair value	(78,672)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 5.00% 2012-07 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(43,800)	[1],[2]
Description	Federal National Mortgage Association (30 Year)	[1],[2]
Rate	5.00%	[1],[2]
Investments maturity date	2012-07	[1],[2]
Fair value	(47,407)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 5.00% 2012-08 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(25,000)	[1],[2]
Description	Federal National Mortgage Association (30 Year)	[1],[2]
Rate	5.00%	[1],[2]
Investments maturity date	2012-08	[1],[2]
Fair value	(27,053)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal Home Loan Mortgage Corporation (30 Year) 5.00% 2012-07 [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	2012-07	[1],[2]
Fair value	(17,737)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (15 Year) 4.00% 2012-07 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(16,300)	[1],[2]
Description	Federal National Mortgage Association (15 Year)	[1],[2]
Rate	4.00%	[1],[2]
Investments maturity date	2012-07	[1],[2]
Fair value	(17,336)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 5.50% 2012-07 [Member]
Investments Sold, Not yet Purchased [Line Items]
Current Principal/Notional Amount	(13,500)	[1],[2]
Description	Federal National Mortgage Association (30 Year)	[1],[2]
Rate	5.50%	[1],[2]
Investments maturity date	2012-07	[1],[2]
Fair value	(14,726)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (15 Year) 4.50% 2012-07 [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	2012-07	[1],[2]
Fair value	(11,791)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Federal National Mortgage Association (30 Year) 6.00% 2012-07 [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	2012-07	[1],[2]
Fair value	(2,748)	[1],[2]
TBA - Fixed Rate Agency Securities Sold Short [Member] | Other Federal Home Loan Mortgage Corporation (30 Year) 6.00% 2012-07 [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	2012-07	[1],[2]
Fair value	(1,097)	[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]
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]
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]
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]
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]
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]
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]
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]
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]
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]
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]
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]
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]
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	4.77%		19.18%
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	111.11%		93.03%
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%

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

[2] At June 30, 2012, the Company's short investments guaranteed by the Federal National Mortgage Association and the Federal Home Loan Mortgage Corporation represented 111.11% and 4.77% 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.