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Financing Agreements - Financing Agreements (Details) - USD ($) $ in Thousands | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Financing Agreements [Line Items] |  |
Unpaid Principal Balance | $ 6,377,370 | $ 4,339,479
Fair value / Carrying Value | 6,378,782 | 4,336,976
Held at Carrying Value |  |
Financing Agreements [Line Items] |  |
Unpaid Principal Balance | 3,123,070 | 978,300
Fair value / Carrying Value | 3,112,009 | 970,204
Fair Value |  |
Financing Agreements [Line Items] |  |
Unpaid Principal Balance | 3,254,300 | 3,361,179
Amortized Cost Balance | 3,267,981 | 3,352,529
Fair value / Carrying Value | 3,266,773 | 3,366,772
Agreements with mark-to-market collateral provisions | Held at Carrying Value |  |
Financing Agreements [Line Items] |  |
Unpaid Principal Balance | 1,240,510 |
Fair value / Carrying Value | 1,239,937 |
Agreements with mark-to-market collateral provisions | Fair Value |  |
Financing Agreements [Line Items] |  |
Unpaid Principal Balance | 1,322,362 | 1,156,899
Amortized Cost Balance | 1,322,362 | 1,156,899
Fair value / Carrying Value | 1,322,362 | 1,159,213
Agreements with non-mark-to-market collateral provisions | Held at Carrying Value |  |
Financing Agreements [Line Items] |  |
Unpaid Principal Balance | 311,977 |
Fair value / Carrying Value | 311,260 |
Agreements with non-mark-to-market collateral provisions | Fair Value |  |
Financing Agreements [Line Items] |  |
Unpaid Principal Balance | 627,026 | 1,338,077
Amortized Cost Balance | 627,026 | 1,338,077
Fair value / Carrying Value | 628,280 | 1,338,077
Securitized debt | Held at Carrying Value |  |
Financing Agreements [Line Items] |  |
Unpaid Principal Balance | 1,340,583 | 648,300
Fair value / Carrying Value | 1,334,342 | 645,027
Securitized debt | Fair Value |  |
Financing Agreements [Line Items] |  |
Unpaid Principal Balance | 1,304,912 | 866,203
Amortized Cost Balance | 1,318,593 | 857,553
Fair value / Carrying Value | 1,316,131 | 869,482
Convertible senior notes | Held at Carrying Value |  |
Financing Agreements [Line Items] |  |
Unpaid Principal Balance | 230,000 | 230,000
Fair value / Carrying Value | $ 226,470 | 225,177
Senior Notes | Held at Carrying Value |  |
Financing Agreements [Line Items] |  |
Unpaid Principal Balance |  | 100,000
Fair value / Carrying Value |  | $ 100,000

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