Quarterly report pursuant to Section 13 or 15(d)

Schedule of Underlying Assets of Repurchase Agreements when Amount of Repurchase Agreements Exceeds 10 Percent of Assets (Details)

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Schedule of Underlying Assets of Repurchase Agreements when Amount of Repurchase Agreements Exceeds 10 Percent of Assets (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Assets Sold under Agreements to Repurchase [Line Items]    
Assets pledged or restricted as collateral for repurchase agreements $ 20,451,045 $ 10,753,868
Available-for-sale Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets pledged or restricted as collateral for repurchase agreements 17,940,144 9,540,849
Commercial Real Estate Assets [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets pledged or restricted as collateral for repurchase agreements 1,997,077 648,885
Retained Interest [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets pledged or restricted as collateral for repurchase agreements 224,394 211,095
Cash and Cash Equivalents [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets pledged or restricted as collateral for repurchase agreements 14,796 15,000
Restricted Cash and Cash Equivalents [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets pledged or restricted as collateral for repurchase agreements 149,845 162,759
Due From Correspondent Brokers [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets pledged or restricted as collateral for repurchase agreements 23,602 48,939
Derivative Financial Instruments, Assets [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets pledged or restricted as collateral for repurchase agreements $ 101,187 $ 126,341