Annual report pursuant to Section 13 and 15(d)

Derivative Instruments and Hedging Activities Interest Rate Sensitive Assets/Liabilities (Details)

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Derivative Instruments and Hedging Activities Interest Rate Sensitive Assets/Liabilities (Details) (USD $)
Dec. 31, 2011
Dec. 31, 2010
Derivatives, Fair Value [Line Items]    
Available-for-sale Securities, Interest-only $ 48,400,000 $ 18,400,000
Trading Securities 1,003,301,000 199,523,000
Derivative Asset, Fair Value, Gross Asset 251,856,000 38,109,000
Derivative Liability, Fair Value, Gross Liability 49,080,000 158,000
Agency To-be-Announced Securities, Notional Amount, Long 275,000,000  
Agency To-be-Announced Securities, Notional Amount, Short 850,000,000  
Agency To-be-Announced Securities, Fair Value, Asset 2,700,000  
Agency To-be-Announced Securities, Fair Value, Liability (5,700,000)  
Forward Sale Commitment, Notional Amount $ 5,200,000