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Financing Agreements (Financing Agreements) (Details) - USD ($) $ in Thousands | Sep. 30, 2020 | Jun. 30, 2020 | Jun. 26, 2020 | Dec. 31, 2019
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Financing Agreements [Line Items] |  |  |  |
Unpaid Principal Balance | $ 4,864,554 |  |  | $ 10,044,844
Fair value / Carrying Value | 4,851,121 |  |  | 10,031,606
Financing agreements with non-mark-to-market collateral provisions |  |  |  |
Financing Agreements [Line Items] |  |  |  |
Unpaid Principal Balance | 1,723,959 |  |  |
Amortized Cost Balance | 1,723,959 |  |  |
Fair value / Carrying Value | 1,727,407 |  |  |
Financing agreements with mark-to-market collateral provisions |  |  |  |
Financing Agreements [Line Items] |  |  |  |
Unpaid Principal Balance | 1,489,097 |  |  |
Amortized Cost Balance | 1,489,097 |  |  |
Fair value / Carrying Value | 1,490,271 |  | $ 1,650,000 |
Senior secured credit agreement |  |  |  |
Financing Agreements [Line Items] |  |  |  |
Unpaid Principal Balance | 481,250 | $ 500,000 |  |
Amortized Cost Balance | 462,923 |  |  |
Fair value / Carrying Value | 473,993 |  |  |
Securitized debt |  |  |  |
Financing Agreements [Line Items] |  |  |  |
Unpaid Principal Balance | 389,051 |  |  | 573,900
Amortized Cost Balance | 380,407 |  |  |
Fair value / Carrying Value | 388,790 |  |  | 570,952
Total Financing agreements, at fair value |  |  |  |
Financing Agreements [Line Items] |  |  |  |
Unpaid Principal Balance | 4,083,357 |  |  |
Amortized Cost Balance | 4,056,386 |  |  |
Fair value / Carrying Value | 4,080,461 |  |  |
Repurchase agreements |  |  |  |
Financing Agreements [Line Items] |  |  |  |
Unpaid Principal Balance |  |  |  | 9,140,944
Fair value / Carrying Value |  |  |  | 9,139,821
Securitized debt |  |  |  |
Financing Agreements [Line Items] |  |  |  |
Unpaid Principal Balance | 451,197 |  |  |
Fair value / Carrying Value | 448,893 |  |  |
Convertible senior notes |  |  |  |
Financing Agreements [Line Items] |  |  |  |
Unpaid Principal Balance | 230,000 |  |  | 230,000
Fair value / Carrying Value | 224,867 |  |  | 223,971
Senior notes |  |  |  |
Financing Agreements [Line Items] |  |  |  |
Unpaid Principal Balance | 100,000 |  |  | 100,000
Fair value / Carrying Value | 96,900 |  |  | $ 96,862
Total Financing agreements at carrying value |  |  |  |
Financing Agreements [Line Items] |  |  |  |
Unpaid Principal Balance | 781,197 |  |  |
Fair value / Carrying Value | $ 770,660 |  |  |

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- Definition Financing Agreements, Amortized Cost + References No definition available. + Details
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