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Derivatives Volume of Activity (Details) $ in Thousands | 6 Months Ended
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Jun. 30, 2019 USD ($)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Interest rate swaps |  |
Derivative [Line Items] |  |
Beginning of Period Notional Amount | $ 4,515,000 | [1]
Notional Amount of Derivative Instruments Added | 2,955,000 |
Notional Amount of Derivative Instruments Maturing, Settled, Terminated, or Paired-Off | (3,970,000) |
End of Period Notional Amount | 3,500,000 | [1]
Not Designated as Hedging Instrument, Economic Hedge [Member] | Eurodollar futures |  |
Derivative [Line Items] |  |
Beginning of Period Notional Amount | 0 |
Notional Amount of Derivative Instruments Added | 3,000,000 |
Notional Amount of Derivative Instruments Maturing, Settled, Terminated, or Paired-Off | 0 |
End of Period Notional Amount | 3,000,000 |
Not Designated as Hedging Instrument, Economic Hedge [Member] | U.S. Treasury futures |  |
Derivative [Line Items] |  |
Beginning of Period Notional Amount | 50,000 |
Notional Amount of Derivative Instruments Added | 0 |
Notional Amount of Derivative Instruments Maturing, Settled, Terminated, or Paired-Off | (50,000) |
End of Period Notional Amount | 0 |
Not Designated as Hedging Instrument, Trading | TBA securities | Long [Member] |  |
Derivative [Line Items] |  |
Beginning of Period Notional Amount | 860,000 |
Notional Amount of Derivative Instruments Added | 4,830,000 |
Notional Amount of Derivative Instruments Maturing, Settled, Terminated, or Paired-Off | (5,320,000) |
End of Period Notional Amount | $ 370,000 |
[1] | The notional amounts include $0 and $775,000 of forward starting pay-fixed interest rate swaps as of June 30, 2019 and December 31, 2018, respectively.

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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