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Fair Value - Schedule of Principal Amounts and Fair Values of the Company’s Borrowings (Details) € in Thousands, £ in Thousands, $ in Thousands	Sep. 30, 2025 USD ($)	Sep. 30, 2025 EUR (€)	Sep. 30, 2025 GBP (£)	Dec. 31, 2024 USD ($)	Dec. 31, 2024 EUR (€)	Dec. 31, 2024 GBP (£)
Principal Amount
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Borrowings	$ 1,784,077			$ 1,872,307
Principal Amount | Unsecured Notes
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Borrowings	990,000			990,000
Principal Amount | Line of Credit | Revolving Credit Facility | Holdings Credit Facility
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Borrowings	308,063			294,363
Principal Amount | Line of Credit | Revolving Credit Facility | NMFC Credit Facility
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Borrowings	31,032	€ 16,512	£ 8,666	27,944	€ 16,512	£ 8,666
Principal Amount | 2022 Convertible Notes
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Borrowings	258,777			260,000
Principal Amount | SBA-guaranteed debentures
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Borrowings	196,205			300,000
Fair Value
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Borrowings	1,775,934			1,849,230
Fair Value | Unsecured Notes
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Borrowings	1,004,496			991,624
Fair Value | Line of Credit | Revolving Credit Facility | Holdings Credit Facility
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Borrowings	307,999			298,435
Fair Value | Line of Credit | Revolving Credit Facility | NMFC Credit Facility
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Borrowings	30,969	€ 16,477	£ 8,650	26,812	€ 15,379	£ 8,700
Fair Value | 2022 Convertible Notes
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Borrowings	259,036			261,811
Fair Value | SBA-guaranteed debentures
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Borrowings	$ 173,434			$ 270,548

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- Definition

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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