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Mortgage-Backed Securities (Details) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2021 USD ($) plantiff | Sep. 30, 2020 USD ($) | Sep. 30, 2021 USD ($) plantiff | Sep. 30, 2020 USD ($) | Dec. 31, 2020 USD ($) plantiff
Investments [Line Items] |  |  |  |  |  |  |  |
Par value of available for sale debt security | $ 1,458,293,000 |  |  | $ 1,458,293,000 |  |  | $ 2,076,346,000 |
Investments, Unamortized Premium (Discount) | 344,027,000 |  |  | 344,027,000 |  |  | 439,648,000 |
Debt Securities, Available-for-sale, Amortized Cost | 1,802,320,000 |  |  | 1,802,320,000 |  |  | 2,515,994,000 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 34,317,000 |  |  | 34,317,000 |  |  | 81,293,000 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (14,081,000) |  |  | (14,081,000) |  |  | (1,032,000) |
Debt Securities, Available-for-sale | 1,822,556,000 |  |  | 1,822,556,000 |  |  | 2,596,255,000 |
Par Value of Debt Security, Fair Value Option Elected | 1,000,854,000 |  |  | 1,000,854,000 |  |  |  |
Debt Securities, Trading, Amortized Cost | 1,038,700,000 |  |  | 1,038,700,000 |  |  |  |
Debt Securities, Trading, Unrealized Gain |  |  |  | 69,000 |  |  |  |
Debt Securities, Trading, Unrealized Loss |  |  |  | (3,159,000) |  |  |  |
Debt Securities, Trading | 1,035,610,000 |  |  | 1,035,610,000 |  |  |  |
Debt Securities, Trading and Available-for-sale | 2,858,166,000 |  |  | 2,858,166,000 |  |  |  |
Proceeds Received | 0 |  | $ 403,095,000 | 325,282,000 |  | $ 4,403,054,000 |  |
Realized Gain (Loss) | 0 |  | 20,846,000 | 6,705,000 |  | 298,728,000 |  |
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 |  |  | 0 |  |  |  |
Fair Value Option |  |  |  |  |  |  |  |
Investments [Line Items] |  |  |  |  |  |  |  |
Investments, Unamortized Premium (Discount) | 37,846,000 |  |  | 37,846,000 |  |  |  |
Residential Mortgage Backed Securities |  |  |  |  |  |  |  |
Investments [Line Items] |  |  |  |  |  |  |  |
Par value of available for sale debt security |  |  |  |  |  |  | 1,839,046,000 |
Investments, Unamortized Premium (Discount) |  |  |  |  |  |  | 57,997,000 |
Debt Securities, Available-for-sale, Amortized Cost |  |  |  |  |  |  | 1,897,043,000 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax |  |  |  |  |  |  | 49,348,000 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax |  |  |  |  |  |  | 0 |
Debt Securities, Available-for-sale |  |  |  |  |  |  | 1,946,391,000 |
Residential Mortgage Backed Securities | Agency MBS |  |  |  |  |  |  |  |
Investments [Line Items] |  |  |  |  |  |  |  |
Par value of available for sale debt security | 1,271,603,000 |  |  | 1,271,603,000 |  |  |  |
Investments, Unamortized Premium (Discount) | 41,604,000 |  |  | 41,604,000 |  |  |  |
Debt Securities, Available-for-sale, Amortized Cost | 1,313,207,000 |  |  | 1,313,207,000 |  |  |  |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 10,056,000 |  |  | 10,056,000 |  |  |  |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (13,348,000) |  |  | (13,348,000) |  |  |  |
Debt Securities, Available-for-sale | 1,309,915,000 |  |  | 1,309,915,000 |  |  | 1,946,391,000 |
Par Value of Debt Security, Fair Value Option Elected | 1,000,854,000 |  |  | 1,000,854,000 |  |  |  |
Debt Securities, Trading, Amortized Cost | 1,034,387,000 |  |  | 1,034,387,000 |  |  |  |
Debt Securities, Trading, Unrealized Gain |  |  |  | 52,000 |  |  |  |
Debt Securities, Trading, Unrealized Loss |  |  |  | (3,132,000) |  |  |  |
Debt Securities, Trading | 1,031,307,000 |  |  | 1,031,307,000 |  |  |  |
Debt Securities, Trading and Available-for-sale | 2,341,222,000 |  |  | 2,341,222,000 |  |  |  |
Proceeds Received | 0 |  | 0 | 287,409,000 |  | 2,187,956,000 |  |
Realized Gain (Loss) | 0 |  | 1,000 | 3,938,000 |  | 75,824,000 |  |
Residential Mortgage Backed Securities | Agency MBS | Fair Value Option |  |  |  |  |  |  |  |
Investments [Line Items] |  |  |  |  |  |  |  |
Investments, Unamortized Premium (Discount) | 33,533,000 |  |  | 33,533,000 |  |  |  |
Commercial Mortgage Backed Securities |  |  |  |  |  |  |  |
Investments [Line Items] |  |  |  |  |  |  |  |
Investments, Unamortized Premium (Discount) |  |  |  |  |  |  | 3,152,000 |
Debt Securities, Available-for-sale, Amortized Cost |  |  |  |  |  |  | 238,953,000 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax |  |  |  |  |  |  | 19,597,000 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax |  |  |  |  |  |  | 0 |
Debt Securities, Available-for-sale |  |  |  |  |  |  | 258,550,000 |
Proceeds Received | 0 |  |  | 37,873,000 |  |  |  |
Realized Gain (Loss) | 0 |  |  | 2,767,000 |  |  |  |
Commercial Mortgage Backed Securities | Agency MBS |  |  |  |  |  |  |  |
Investments [Line Items] |  |  |  |  |  |  |  |
Par value of available for sale debt security | 185,603,000 |  |  | 185,603,000 |  |  | 235,801,000 |
Investments, Unamortized Premium (Discount) | 2,608,000 |  |  | 2,608,000 |  |  |  |
Debt Securities, Available-for-sale, Amortized Cost | 188,211,000 |  |  | 188,211,000 |  |  |  |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 10,230,000 |  |  | 10,230,000 |  |  |  |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (7,000) |  |  | (7,000) |  |  |  |
Debt Securities, Available-for-sale | 198,434,000 |  |  | 198,434,000 |  |  | 258,550,000 |
Debt Securities, Trading and Available-for-sale | 198,434,000 |  |  | 198,434,000 |  |  |  |
Proceeds Received |  |  | 403,095,000 |  |  | 2,215,098,000 |  |
Realized Gain (Loss) |  |  | $ (20,845,000) |  |  | $ 222,904,000 |  |
Interest-Only-Strip |  |  |  |  |  |  |  |
Investments [Line Items] |  |  |  |  |  |  |  |
Par value of available for sale debt security | 0 | [1] |  | 0 | [1] |  | 0 | [2]
Investments, Unamortized Premium (Discount) | 300,061,000 |  |  | 300,061,000 |  |  | 378,939,000 |
Debt Securities, Available-for-sale, Amortized Cost | 300,061,000 |  |  | 300,061,000 |  |  | 378,939,000 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 13,924,000 |  |  | 13,924,000 |  |  | 12,081,000 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (684,000) |  |  | (684,000) |  |  | (981,000) |
Debt Securities, Available-for-sale | 313,301,000 |  |  | 313,301,000 |  |  | 390,039,000 |
Debt Securities, Trading, Amortized Cost | 4,313,000 |  |  | 4,313,000 |  |  |  |
Debt Securities, Trading, Unrealized Gain |  |  |  | 17,000 |  |  |  |
Debt Securities, Trading, Unrealized Loss |  |  |  | (27,000) |  |  |  |
Debt Securities, Trading | 4,303,000 |  |  | 4,303,000 |  |  |  |
Debt Securities, Trading and Available-for-sale | 317,604,000 |  |  | 317,604,000 |  |  |  |
Interest-Only-Strip | Fair Value Option |  |  |  |  |  |  |  |
Investments [Line Items] |  |  |  |  |  |  |  |
Investments, Unamortized Premium (Discount) | 4,313,000 |  |  | 4,313,000 |  |  |  |
Par Value of Debt Security, Fair Value Option Elected | 0 |  |  | 0 |  |  |  |
Non-Agency MBS |  |  |  |  |  |  |  |
Investments [Line Items] |  |  |  |  |  |  |  |
Par value of available for sale debt security | 1,087,000 |  |  | 1,087,000 |  |  | 1,499,000 |
Investments, Unamortized Premium (Discount) | (246,000) |  |  | (246,000) |  |  | (440,000) |
Debt Securities, Available-for-sale, Amortized Cost | 841,000 |  |  | 841,000 |  |  | 1,059,000 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 107,000 |  |  | 107,000 |  |  | 267,000 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (42,000) |  |  | (42,000) |  |  | (51,000) |
Debt Securities, Available-for-sale | 906,000 |  |  | 906,000 |  |  | 1,275,000 |
Debt Securities, Trading and Available-for-sale | 906,000 |  |  | 906,000 |  |  |  |
Notional balance for interest only securities | 8,865,021,000 |  |  | 8,865,021,000 |  |  | 9,319,520,000 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 10,153,000 |  |  | 10,153,000 |  |  | 33,417,000 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 2,771,000 |  |  | 2,771,000 |  |  | 2,156,000 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (159,000) |  |  | (159,000) |  |  | (408,000) |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | $ (159,000) |  |  | $ (159,000) |  |  | $ (93,000) |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | 12 |  |  | 12 |  |  | 23 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | plantiff | 7 |  |  | 7 |  |  | 5 |
Agency MBS |  |  |  |  |  |  |  |
Investments [Line Items] |  |  |  |  |  |  |  |
Notional balance for interest only securities | $ 10,508,786,000 |  |  | $ 10,508,786,000 |  |  | $ 11,277,908,000 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 1,121,823,000 |  |  | 1,121,823,000 |  |  | 19,266,000 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 24,000 |  |  | 24,000 |  |  | 749,000 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (13,738,000) |  |  | (13,738,000) |  |  | (399,000) |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | $ (26,000) |  |  | $ (26,000) |  |  | $ (133,000) |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | plantiff | 23 |  |  | 23 |  |  | 19 |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | 1 |  |  | 1 |  |  | 2 |
[1] | The notional balance for Agency CMBS IO and non-Agency CMBS IO was $10,508,786 and $8,865,021 respectively, as of September 30, 2021.
[2] | The notional balance for the Agency CMBS IO and non-Agency CMBS IO was $11,277,908 and $9,319,520, respectively, as of December 31, 2020.

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