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) (Interest Rate Swaps Associated with TBA Contracts [Member], USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Derivative [Line Items]  
Derivative, Notional Amount $ 500,000
Derivative Maturity Over Two And Within Three Years From Balance Sheet Date [Member]
 
Derivative [Line Items]  
Derivative, Notional Amount $ 500,000
Derivative, Average Fixed Interest Rate 0.399%
Derivative, Average Variable Interest Rate 0.356%
Derivative, Weighted Average Remaining Maturity 1.775