Quarterly report pursuant to Section 13 or 15(d)

Repurchase Agreements Schedule of Underlying Assets of Repurchase Agreements when Amount of Repurchase Agreements Exceeds 10 Percent of Assets (Details)

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Repurchase Agreements Schedule of Underlying Assets of Repurchase Agreements when Amount of Repurchase Agreements Exceeds 10 Percent of Assets (Details) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Market Value $ 15,842,420 $ 7,457,095
Available-for-sale Securities [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Market Value 14,453,848 6,160,229
US Treasury Securities [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Market Value 1,002,461 1,003,301
Loans Held-for-sale, Mortgages [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Market Value 14,553 5,782
Cash and Cash Equivalents [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Market Value 10,000 15,000
Restricted Cash and Cash Equivalents [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Market Value 14,018 94,803
Due From Correspondent Brokers [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Market Value 28,965 32,201
Derivative Financial Instruments, Assets [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Market Value $ 318,575 $ 145,779