Quarterly report pursuant to Section 13 or 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 $)
Mar. 31, 2012
Dec. 31, 2011
Derivatives, Fair Value [Line Items]    
Available-for-sale Securities, Interest-only $ 60,600,000 $ 48,400,000
Agency To-be-Announced Securities, Notional Amount, Long 500,000,000 275,000,000
Agency To-be-Announced Securities, Notional Amount, Short 2,000,000,000 850,000,000
Agency To-be-Announced Securities, Fair Value, Asset 1,500,000 2,700,000
Agency To-be-Announced Securities, Fair Value, Liability (3,100,000) (5,700,000)
Forward Sale Commitment, Notional Amount 5,200,000  
Trading Securities 1,002,090,000 1,003,301,000
Derivative Asset, Fair Value, Gross Asset 340,715,000 251,856,000
Derivative Liability, Fair Value, Gross Liability 47,475,000 49,080,000
Derivative Financial Instruments, Assets [Member]
   
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Net 340,715,000 251,856,000
Forward Sale Commitment [Member] | Derivative Financial Instruments, Assets [Member]
   
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Net $ 26,701 $ 0