Quarterly report pursuant to Section 13 or 15(d)

Available-for-Sale Securities, at Fair Value Available-for-Sale Securities Sold Under Agreements to Repurchase (Details)

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Available-for-Sale Securities, at Fair Value Available-for-Sale Securities Sold Under Agreements to Repurchase (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