Annual report pursuant to Section 13 and 15(d)

Derivative Instruments and Hedging Activities Schedule of Interest Rate Swaps Associated with Repurchase Agreements (Details)

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Derivative Instruments and Hedging Activities Schedule of Interest Rate Swaps Associated with Repurchase Agreements (Details) (Swap [Member], USD $)
In Thousands, unless otherwise specified
Dec. 31, 2011
Dec. 31, 2010
Derivative [Line Items]    
Derivative, Notional Amount $ 4,385,000 $ 650,000
Derivative, Average Fixed Interest Rate 0.9523% 1.526%
Derivative, Average Variable Interest Rate 0.3611% 0.306%
Derivative, Average Remaining Maturity 2.406 3.294
One Year from Balance Sheet Date [Member]
    
Derivative [Line Items]    
Derivative, Notional Amount 25,000 100,000
Derivative, Average Fixed Interest Rate 0.8675% 1.168%
Derivative, Average Variable Interest Rate 0.315% 0.3425%
Derivative, Average Remaining Maturity .975 .9583
More than One and within Two Years from Balance Sheet Date [Member]
    
Derivative [Line Items]    
Derivative, Notional Amount 2,025,000 25,000
Derivative, Average Fixed Interest Rate 0.7366% 0.8675%
Derivative, Average Variable Interest Rate 0.368% 0.308%
Derivative, Average Remaining Maturity 1.55 1.975
More than Two and within Three Years from Balance Sheet Date [Member]
    
Derivative [Line Items]    
Derivative, Notional Amount 1,275,000 175,000
Derivative, Average Fixed Interest Rate 0.6699% 1.376%
Derivative, Average Variable Interest Rate 0.3801% 0.3055%
Derivative, Average Remaining Maturity 2.719 2.613
More than Three and within Four Years from Balance Sheet Date [Member]
    
Derivative [Line Items]    
Derivative, Notional Amount 820,000 175,000
Derivative, Average Fixed Interest Rate 1.5747% 1.671%
Derivative, Average Variable Interest Rate 0.329% 0.3026%
Derivative, Average Remaining Maturity 3.524 3.956
More than Four and within Five Years from Balance Sheet Date [Member]
    
Derivative [Line Items]    
Derivative, Notional Amount $ 240,000 $ 175,000
Derivative, Average Fixed Interest Rate 2.1556% 1.83%
Derivative, Average Variable Interest Rate 0.3158% 0.2874%
Derivative, Average Remaining Maturity 4.322 4.837