Quarterly report pursuant to Section 13 or 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
Jun. 30, 2012
Dec. 31, 2011
Assets Sold under Agreements to Repurchase [Line Items]    
Due to Correspondent Brokers $ 166,949 $ 45,565
Assets Sold under Agreements to Repurchase, Repurchase Liability 10,438,441 6,660,148
Assets Sold under Agreements to Repurchase, Weighted Average Borrowing Rate, Excluding U.S. Treasuries and Interest Rate Swaps 0.71% 0.78%
Assets Sold under Agreements to Repurchase, Weighted Average Remaining Maturity, Excluding U.S. Treasuries and Interest Rate Swaps 86 73
Securities Sold under Agreements to Repurchase 10,438,441 6,660,148
Assets Sold under Agreements to Repurchase, Interest Rate 0.67% 0.68%
US Treasury Securities [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 997,500 1,001,250
Assets Sold under Agreements to Repurchase, Interest Rate 0.24% 0.12%
US Government Agencies Debt Securities [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 8,112,340 4,804,533
Assets Sold under Agreements to Repurchase, Interest Rate 0.47% 0.50%
Mortgage-backed Securities, Issued by Private Enterprises [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 1,121,990 731,014
Assets Sold under Agreements to Repurchase, Interest Rate 2.38% 2.61%
Inverse Interest-Only Securities [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 202,247 118,032
Assets Sold under Agreements to Repurchase, Interest Rate 1.16% 0.97%
Loans Held-for-sale, Mortgages [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability $ 4,364 $ 5,319
Assets Sold under Agreements to Repurchase, Interest Rate 2.50% 3.20%