Debt - Schedule of Available and Outstanding Debt (Details) - USD ($) |
Dec. 31, 2023 |
Dec. 31, 2022 |
Jun. 23, 2022 |
Jun. 22, 2022 |
Jan. 20, 2022 |
Sep. 16, 2021 |
Mar. 04, 2021 |
Nov. 04, 2020 |
Jun. 03, 2020 |
Feb. 05, 2020 |
Jul. 16, 2019 |
Sep. 24, 2018 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Debt Instrument [Line Items] | ||||||||||||
| Outstanding balance | $ 2,215,000,000 | $ 2,185,000,000 | ||||||||||
| Principal | 1,570,000,000 | 1,594,000,000 | ||||||||||
| Carrying Value | 1,554,869,000 | 1,574,351,000 | ||||||||||
| SBA Debentures | ||||||||||||
| Debt Instrument [Line Items] | ||||||||||||
| Outstanding balance | 175,000,000 | 175,000,000 | ||||||||||
| Principal | 175,000,000 | 175,000,000 | ||||||||||
| Carrying Value | 170,323,000 | 169,738,000 | ||||||||||
| July 2024 Notes | ||||||||||||
| Debt Instrument [Line Items] | ||||||||||||
| Outstanding balance | 105,000,000 | 105,000,000 | $ 105,000,000 | |||||||||
| Principal | 105,000,000 | 105,000,000 | ||||||||||
| Carrying Value | 104,828,000 | 104,533,000 | ||||||||||
| February 2025 Notes | ||||||||||||
| Debt Instrument [Line Items] | ||||||||||||
| Outstanding balance | 50,000,000 | 50,000,000 | $ 50,000,000 | |||||||||
| Principal | 50,000,000 | 50,000,000 | ||||||||||
| Carrying Value | 49,866,000 | 49,751,000 | ||||||||||
| June 2025 Notes | ||||||||||||
| Debt Instrument [Line Items] | ||||||||||||
| Outstanding balance | 70,000,000 | 70,000,000 | $ 70,000,000 | |||||||||
| Principal | 70,000,000 | 70,000,000 | ||||||||||
| Carrying Value | 69,757,000 | 69,595,000 | ||||||||||
| June 2025 3-Year Notes | ||||||||||||
| Debt Instrument [Line Items] | ||||||||||||
| Outstanding balance | 50,000,000 | 50,000,000 | $ 50,000,000 | |||||||||
| Principal | 50,000,000 | 50,000,000 | ||||||||||
| Carrying Value | 49,771,000 | 49,616,000 | ||||||||||
| March 2026 A Notes | ||||||||||||
| Debt Instrument [Line Items] | ||||||||||||
| Outstanding balance | 50,000,000 | 50,000,000 | $ 50,000,000 | |||||||||
| Principal | 50,000,000 | 50,000,000 | ||||||||||
| Carrying Value | 49,795,000 | 49,700,000 | ||||||||||
| March 2026 B Notes | ||||||||||||
| Debt Instrument [Line Items] | ||||||||||||
| Outstanding balance | 50,000,000 | 50,000,000 | $ 50,000,000 | |||||||||
| Principal | 50,000,000 | 50,000,000 | ||||||||||
| Carrying Value | 49,776,000 | 49,673,000 | ||||||||||
| September 2026 Notes | ||||||||||||
| Debt Instrument [Line Items] | ||||||||||||
| Outstanding balance | 325,000,000 | 325,000,000 | $ 325,000,000 | |||||||||
| Principal | 325,000,000 | 325,000,000 | ||||||||||
| Carrying Value | 322,339,000 | 321,358,000 | ||||||||||
| January 2027 Notes | ||||||||||||
| Debt Instrument [Line Items] | ||||||||||||
| Outstanding balance | 350,000,000 | 350,000,000 | $ 350,000,000 | |||||||||
| Principal | 350,000,000 | 350,000,000 | ||||||||||
| Carrying Value | 345,935,000 | 344,604,000 | ||||||||||
| 2031 Asset-Backed Notes | ||||||||||||
| Debt Instrument [Line Items] | ||||||||||||
| Outstanding balance | 150,000,000 | 150,000,000 | $ 150,000,000 | |||||||||
| Principal | 150,000,000 | 150,000,000 | ||||||||||
| Carrying Value | 148,544,000 | 147,957,000 | ||||||||||
| 2033 Notes | ||||||||||||
| Debt Instrument [Line Items] | ||||||||||||
| Outstanding balance | 40,000,000 | 40,000,000 | $ 40,000,000 | |||||||||
| Principal | 40,000,000 | 40,000,000 | ||||||||||
| Carrying Value | 38,935,000 | 38,826,000 | ||||||||||
| MUFG Bank Facility | ||||||||||||
| Debt Instrument [Line Items] | ||||||||||||
| Outstanding balance | 400,000,000 | 545,000,000 | ||||||||||
| Principal | 61,000,000 | 107,000,000 | ||||||||||
| Carrying Value | 61,000,000 | 107,000,000 | ||||||||||
| SMBC Facility | ||||||||||||
| Debt Instrument [Line Items] | ||||||||||||
| Outstanding balance | 400,000,000 | 225,000,000 | ||||||||||
| Principal | 94,000,000 | 72,000,000 | ||||||||||
| Carrying Value | $ 94,000,000 | $ 72,000,000 |