Annual report pursuant to Section 13 and 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
Dec. 31, 2012
Dec. 31, 2011
Repurchase Agreement Counterparty [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability $ 12,624,510 $ 6,660,148
Repurchase Agreement Counterparty, JP Morgan Chase [Member]
   
Repurchase Agreement Counterparty [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 1,382,348 1,250,629
Repurchase Agreement Counterparty, Amount at Risk 281,717 184,046
Repurchase Agreement Counterparty, Percent of Equity at Risk 8.00% 14.00%
Repurchase Agreement Counterparty, Weighted Average Maturity 70.8 69.98
Repurchase Agreement Counterparty, All Other Counterparties [Member]
   
Repurchase Agreement Counterparty [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 10,244,662 4,408,269
Repurchase Agreement Counterparty, Amount at Risk 1,379,409 613,446
Repurchase Agreement Counterparty, Percent of Equity at Risk 40.00% 48.00%
Repurchase Agreement Counterparty, Weighted Average Maturity 86.4 73.78
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 11,627,010 5,658,898
Repurchase Agreement Counterparty, Amount at Risk 1,661,126 797,492
Payables to Broker-Dealers and Clearing Organizations $ 291,675 $ 45,565
Number of Repurchase Agreement Counterparties with Whom Repurchase Agreements Are Less Than 10 Percent of Stockholders' Equity 21 17