Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Schedule of Credit Default Swaps, Provide Protection (Details)

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Derivative Instruments and Hedging Activities Schedule of Credit Default Swaps, Provide Protection (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Mar. 31, 2012
Credit Default Swap, Buying Protection [Member]
Dec. 31, 2011
Credit Default Swap, Buying Protection [Member]
Mar. 31, 2012
Credit Default Swap, Selling Protection [Member]
Dec. 31, 2011
Credit Default Swap, Selling Protection [Member]
Mar. 31, 2012
Maturity Date, 07/25/2036 [Member]
Credit Default Swap, Selling Protection [Member]
Dec. 31, 2011
Maturity Date, 07/25/2036 [Member]
Credit Default Swap, Selling Protection [Member]
Mar. 31, 2012
Maturity Date, 05/25/2046 [Member]
Credit Default Swap, Buying Protection [Member]
Dec. 31, 2011
Maturity Date, 05/25/2046 [Member]
Credit Default Swap, Buying Protection [Member]
Mar. 31, 2012
Maturity Date, 05/25/2046 [Member]
Credit Default Swap, Selling Protection [Member]
Dec. 31, 2011
Maturity Date, 05/25/2046 [Member]
Credit Default Swap, Selling Protection [Member]
Derivative [Line Items]                        
Derivative, Maturity Date             Jul. 25, 2036 Jul. 25, 2036 May 25, 2046 May 25, 2046 May 25, 2046 May 25, 2046
Derivative, Average Basis Spread on Variable Rate     33976.00% 34194.00% 25500.00% 28959.00% 35246.00% 35871.00% 37723.00% 37723.00% 14618.00% 14618.00%
Notional Amount of Derivatives     $ (541,426) $ (544,699) $ 111,450 $ 154,812 $ 58,795 $ 99,890 $ (119,426) $ (119,699) $ 52,655 $ 54,922
Derivative, Fair Value, Net     62,924 86,136 (9,802) (14,638) 3,682 2,733 60,259 67,698 (13,484) (17,371)
Derivative, Cost     (77,091) (77,091) 6,171 2,485 (7,403) (11,089) (57,322) (57,322) 13,574 13,574
Derivative, Gain (Loss) on Derivative, Net $ (8,890) $ 5,347 $ (14,167) $ 9,045 $ (3,631) $ (12,153) $ (3,721) $ (8,356) $ 2,937 $ 10,376 $ 90 $ (3,797)