Quarterly report pursuant to Section 13 or 15(d)

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

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Schedule of Repurchase Agreement Counterparties with Whom Repurchase Agreements Exceed 10 Percent of Stockholders' Equity (Details) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2014
Dec. 31, 2013
Repurchase Agreement Counterparty [Line Items]    
Payables to Broker-Dealers and Clearing Organizations $ 31,055  
Assets Sold under Agreements to Repurchase, Repurchase Liability 12,274,878 12,250,450
Repurchase Agreement Counterparty, Royal Bank of Canada [Member]
    
Repurchase Agreement Counterparty [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 1,280,084 980,464
Repurchase Agreement Counterparty, Amount at Risk 393,951 264,745
Repurchase Agreement Counterparty, Percent of Equity at Risk 10.00% 7.00%
Repurchase Agreement Counterparty, Weighted Average Days to Maturity 93.1 88.2
Repurchase Agreement Counterparty, Barclays Capital [Member]
    
Repurchase Agreement Counterparty [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 1,119,776 1,453,396
Repurchase Agreement Counterparty, Amount at Risk 270,340 302,744
Repurchase Agreement Counterparty, Percent of Equity at Risk 7.00% 8.00%
Repurchase Agreement Counterparty, Weighted Average Days to Maturity 78.9 74.6
Repurchase Agreement Counterparty, All Other Counterparties [Member]
    
Repurchase Agreement Counterparty [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 8,881,268 8,819,090
Repurchase Agreement Counterparty, Amount at Risk 885,887 1,107,341
Repurchase Agreement Counterparty, Percent of Equity at Risk 22.00% 29.00%
Repurchase Agreement Counterparty, Weighted Average Days to Maturity 85.0 71.2
Number of Repurchase Agreement Counterparties with Whom Repurchase Agreements Are Less Than 10 Percent of Stockholders' Equity 23 18
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 11,281,128 11,252,950
Repurchase Agreement Counterparty, Amount at Risk 1,550,178 1,674,830
US Treasury Securities [Member]
    
Repurchase Agreement Counterparty [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 1,986,250  
Maturity on Demand [Member]
    
Repurchase Agreement Counterparty [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability $ 993,750 $ 997,500