Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Schedule of Interest Rate Swaps Associated with TBA Contracts (Details)

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Derivative Instruments and Hedging Activities Schedule of Interest Rate Swaps Associated with TBA Contracts (Details) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Interest Rate Swaps Associated with TBA Contracts [Member]
    
Derivative [Line Items]    
Derivative, Notional Amount   $ 175,000
Swap [Member]
    
Derivative [Line Items]    
Derivative, Notional Amount 8,135,000 4,385,000
Derivative, Average Fixed Interest Rate 0.8695% 0.9523%
Derivative, Average Variable Interest Rate 0.4839% 0.3611%
Derivative, Weighted Average Remaining Maturity 2.553 2.406
Derivative Maturity Over Four And Within Five Years From Balance Sheet Date [Member] | Interest Rate Swaps Associated with TBA Contracts [Member]
    
Derivative [Line Items]    
Derivative, Notional Amount   175,000
Derivative, Average Fixed Interest Rate   0.4196%
Derivative, Average Variable Interest Rate   1.772%
Derivative, Weighted Average Remaining Maturity   4.5778
Derivative Maturity Over Four And Within Five Years From Balance Sheet Date [Member] | Swap [Member]
    
Derivative [Line Items]    
Derivative, Notional Amount $ 2,090,000 $ 240,000
Derivative, Average Fixed Interest Rate 1.0527% 2.1556%
Derivative, Average Variable Interest Rate 0.4761% 0.3158%
Derivative, Weighted Average Remaining Maturity 4.276 4.322