Quarterly report pursuant to Section 13 or 15(d)

Fair Value of Financial Instruments (Details)

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Fair Value of Financial Instruments (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Repurchase agreements $ 18,297,392 $ 9,316,351
Long-term Federal Home Loan Bank Advances 1,998,762  
Maturity Over One Year [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Repurchase agreements $ 1,440,855 $ 185,634