Annual report pursuant to Section 13 and 15(d)

Schedule of Repurchase Agreements by Term, Short or Long (Details)

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Schedule of Repurchase Agreements by Term, Short or Long (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements $ 19,451,207 $ 8,865,184
Maturity up to One Year [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 19,338,707 8,865,184
Maturity Over One Year [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements $ 112,500 $ 0