Quarterly report pursuant to Section 13 or 15(d)

Fair Value of Financial Instruments - Schedule of Fair Value Hierarchy of Outstanding Borrowings (Details)

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Fair Value of Financial Instruments - Schedule of Fair Value Hierarchy of Outstanding Borrowings (Details) - USD ($)
$ in Thousands
Sep. 30, 2024
Dec. 31, 2023
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value $ 1,739,209 $ 1,554,869
Carrying Value    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value 1,739,209 1,554,869
Carrying Value | SBA Debentures    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value 170,763 170,323
Carrying Value | July 2024 Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value   104,828
Carrying Value | February 2025 Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value 49,952 49,866
Carrying Value | June 2025 Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value 69,879 69,757
Carrying Value | June 2025 3-Year Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value 49,887 49,771
Carrying Value | March 2026 A Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value 49,866 49,795
Carrying Value | March 2026 B Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value 49,854 49,776
Carrying Value | September 2026 Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value 323,075 322,339
Carrying Value | January 2027 Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value 346,932 345,935
Carrying Value | 2031 Asset-Backed Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value 148,985 148,544
Carrying Value | 2033 Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value 39,016 38,935
Carrying Value | MUFG Bank Facility    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value 240,000 61,000
Carrying Value | SMBC Facility    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value 201,000 94,000
Fair Value    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 1,680,028 1,450,995
Fair Value | Observable Inputs (Level 2)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 186,508 182,900
Fair Value | Unobservable Inputs (Level 3)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 1,493,520 1,268,095
Fair Value | SBA Debentures    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 155,728 142,011
Fair Value | SBA Debentures | Unobservable Inputs (Level 3)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 155,728 142,011
Fair Value | July 2024 Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value   105,755
Fair Value | July 2024 Notes | Unobservable Inputs (Level 3)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value   105,755
Fair Value | February 2025 Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 49,902 49,144
Fair Value | February 2025 Notes | Unobservable Inputs (Level 3)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 49,902 49,144
Fair Value | June 2025 Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 69,890 67,198
Fair Value | June 2025 Notes | Unobservable Inputs (Level 3)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 69,890 67,198
Fair Value | June 2025 3-Year Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 50,560 48,983
Fair Value | June 2025 3-Year Notes | Unobservable Inputs (Level 3)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 50,560 48,983
Fair Value | March 2026 A Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 48,691 47,702
Fair Value | March 2026 A Notes | Unobservable Inputs (Level 3)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 48,691 47,702
Fair Value | March 2026 B Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 48,726 47,759
Fair Value | March 2026 B Notes | Unobservable Inputs (Level 3)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 48,726 47,759
Fair Value | September 2026 Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 301,311 288,711
Fair Value | September 2026 Notes | Unobservable Inputs (Level 3)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 301,311 288,711
Fair Value | January 2027 Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 327,712 315,832
Fair Value | January 2027 Notes | Unobservable Inputs (Level 3)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 327,712 315,832
Fair Value | 2031 Asset-Backed Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 145,500 142,500
Fair Value | 2031 Asset-Backed Notes | Observable Inputs (Level 2)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 145,500 142,500
Fair Value | 2033 Notes    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 41,008 40,400
Fair Value | 2033 Notes | Observable Inputs (Level 2)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 41,008 40,400
Fair Value | MUFG Bank Facility    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 240,000 61,000
Fair Value | MUFG Bank Facility | Unobservable Inputs (Level 3)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 240,000 61,000
Fair Value | SMBC Facility    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value 201,000 94,000
Fair Value | SMBC Facility | Unobservable Inputs (Level 3)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Approximate Fair Value $ 201,000 $ 94,000