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Derivatives Volume of Activity (Details) - USD ($) $ in Thousands | 9 Months Ended |
--- | --- | ---
Sep. 30, 2021 | Dec. 31, 2020
Not Designated as Hedging Instrument, Economic Hedge | Interest rate swaption |  |
Derivative [Line Items] |  |
Derivative, Notional Amount | $ (750,000) | $ (1,250,000)
Notional Amount of Derivative Instruments Added | (500,000) |
Notional Amount of Derivative Instruments Maturing, Settled, Terminated, or Paired-Off | (1,000,000) |
Not Designated as Hedging Instrument, Economic Hedge | U.S. Treasury futures | Short position |  |
Derivative [Line Items] |  |
Derivative, Notional Amount | (3,540,000) | (825,000)
Notional Amount of Derivative Instruments Added | (11,640,000) |
Notional Amount of Derivative Instruments Maturing, Settled, Terminated, or Paired-Off | (8,925,000) |
Not Designated as Hedging Instrument, Economic Hedge | Options on U.S. Treasury futures | Long position |  |
Derivative [Line Items] |  |
Derivative, Notional Amount | 0 | (500,000)
Notional Amount of Derivative Instruments Added | (2,350,000) |
Notional Amount of Derivative Instruments Maturing, Settled, Terminated, or Paired-Off | (2,850,000) |
Not Designated as Hedging Instrument, Trading | TBA securities | Long position |  |
Derivative [Line Items] |  |
Derivative, Notional Amount | (1,980,000) | $ (1,515,000)
Notional Amount of Derivative Instruments Added | (20,235,000) |
Notional Amount of Derivative Instruments Maturing, Settled, Terminated, or Paired-Off | $ (19,770,000) |

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