v3.19.1
Counterparty Risk (Exposure to Counterparty Risk) (Details) - Counterparty Risk [Member]
$ in Thousands
3 Months Ended
Mar. 31, 2019
USD ($)
counterparty
Cash and Cash Equivalents [Member]  
Concentration Risk [Line Items]  
Amount of Exposure | $ $ 55,876
Number of Counterparties with Exposure | counterparty 7
Percentage of Total Outstanding Unpaid Principal Balance 55.90%
Collateral On Repurchase Agreements Held By Dealers [Member]  
Concentration Risk [Line Items]  
Amount of Exposure | $ $ 1,864,614
Number of Counterparties with Exposure | counterparty 25
Percentage of Total Outstanding Unpaid Principal Balance 16.00%
Due From Broker [Member]  
Concentration Risk [Line Items]  
Amount of Exposure | $ $ 58,145
Number of Counterparties with Exposure | counterparty 17
Percentage of Total Outstanding Unpaid Principal Balance 24.90%
Receivable For Securities Sold [Member]  
Concentration Risk [Line Items]  
Amount of Exposure | $ $ 40,489
Number of Counterparties with Exposure | counterparty 6
Percentage of Total Outstanding Unpaid Principal Balance 29.70%