Annual report pursuant to Section 13 and 15(d)

Repurchase Agreements Schedule of Repurchase Agreements by Collateral Type (Details)

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Repurchase Agreements Schedule of Repurchase Agreements by Collateral Type (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2011
Dec. 31, 2010
Assets Sold under Agreements to Repurchase [Line Items]    
Due to Correspondent Brokers $ 45,565 $ 231,724
Assets Sold under Agreements to Repurchase, Repurchase Liability 6,660,148 1,169,803
Assets Sold under Agreements to Repurchase, Weighted Average Borrowing Rate, Excluding U.S. Treasuries and Interest Rate Swaps 0.78% 0.74%
Assets Sold under Agreements to Repurchase, Weighted Average Remaining Maturity, Excluding U.S. Treasuries and Interest Rate Swaps 73 90
Securities Sold under Agreements to Repurchase 6,660,148 1,169,803
Assets Sold under Agreements to Repurchase, Interest Rate 0.68% 0.66%
US Treasury Securities [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 1,001,250 198,750
Assets Sold under Agreements to Repurchase, Interest Rate 0.12% 0.28%
US Government Agencies Debt Securities [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 4,804,533 745,861
Assets Sold under Agreements to Repurchase, Interest Rate 0.50% 0.37%
Mortgage-backed Securities, Issued by Private Enterprises [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 731,014 201,976
Assets Sold under Agreements to Repurchase, Interest Rate 2.61% 2.05%
Inverse Interest-Only Securities [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 118,032 23,216
Assets Sold under Agreements to Repurchase, Interest Rate 0.97% 1.07%
Loans Held-for-sale, Mortgages [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability $ 5,319 $ 0
Assets Sold under Agreements to Repurchase, Interest Rate 3.20% 0.00%