Quarterly report pursuant to Section 13 or 15(d)

Repurchase Agreements Schedule of Repurchase Agreement Counterparties with Whom Repurchase Agreements Exceed 10 Percent of Stockholders' Equity (Details)

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Repurchase Agreements Schedule of Repurchase Agreement Counterparties with Whom Repurchase Agreements Exceed 10 Percent of Stockholders' Equity (Details) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2013
Dec. 31, 2012
Repurchase Agreement Counterparty [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability $ 14,903,155 $ 12,624,510
Repurchase Agreement Counterparty, Barclays Capital [Member]
    
Repurchase Agreement Counterparty [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 1,408,599 1,127,888
Repurchase Agreement Counterparty, Amount at Risk 240,632 257,858
Repurchase Agreement Counterparty, Percent of Equity at Risk 6.00% 7.00%
Repurchase Agreement Counterparty, Weighted Average Maturity 64.6 90.3
Repurchase Agreement Counterparty, All Other Counterparties [Member]
    
Repurchase Agreement Counterparty [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 12,494,556 10,499,122
Repurchase Agreement Counterparty, Amount at Risk 1,345,743 1,403,268
Repurchase Agreement Counterparty, Percent of Equity at Risk 35.00% 41.00%
Repurchase Agreement Counterparty, Weighted Average Maturity 88.6 84
Repurchase Agreement Counterparty, Excluding Repurchase Agreements Collateralized by U.S. Treasuries [Member]
    
Repurchase Agreement Counterparty [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 13,903,155 11,627,010
Repurchase Agreement Counterparty, Amount at Risk 1,586,375 1,661,126
Payables to Broker-Dealers and Clearing Organizations $ 62,803 $ 291,675
Number of Repurchase Agreement Counterparties with Whom Repurchase Agreements Are Less Than 10 Percent of Stockholders' Equity 19 21