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Fair Value Measurements - Fair Value Hierarchy of Financial Instruments (Details) - USD ($) $ in Thousands | Mar. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | $ 10,439,173 | $ 9,868,440
First lien debt |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 10,287,119 | 9,722,061
Second lien debt |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 41,515 | 41,515
Unsecured debt |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 11,859 | 9,924
Investments in equity |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 98,680 | 94,940
Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 0 | 0
Level 1 | First lien debt |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 0 | 0
Level 1 | Second lien debt |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 0 | 0
Level 1 | Unsecured debt |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 0 | 0
Level 1 | Investments in equity |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 0 | 0
Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 108,808 | 157,858
Level 2 | First lien debt |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 108,808 | 157,858
Level 2 | Second lien debt |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 0 | 0
Level 2 | Unsecured debt |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 0 | 0
Level 2 | Investments in equity |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 0 | 0
Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 10,330,365 | 9,710,582
Level 3 | First lien debt |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 10,178,311 | 9,564,203
Level 3 | Second lien debt |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 41,515 | 41,515
Level 3 | Unsecured debt |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | 11,859 | 9,924
Level 3 | Investments in equity |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total | $ 98,680 | $ 94,940

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- Definition Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482106/820-10-50-2 + Details
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