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Fair Value Measurements - Summary of Changes in Fair Value of Investments Measured Using Level 3 Inputs (Details) - USD ($) $ in Thousands | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2024 | Mar. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2022
Total Investments |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair value, beginning of period | $ 10,330,365 | $ 9,426,489 | $ 9,710,582 | $ 9,472,796
Purchases of investments | 739,127 | 114,640 |  |
Proceeds from principal repayments and sales of investments | (186,370) | (71,040) |  |
Accretion of discount/(amortization of premium) | 9,375 | 8,443 |  |
Transfers into Level 3 | 50,239 | 4,938 |  |
Transfers out of Level 3 | 0 | (91,939) |  |
Fair value, end of period | 10,330,365 | 9,426,489 |  |
Net change in unrealized appreciation (depreciation) included in earnings related to financial instruments, included in net unrealized appreciation (depreciation) on the consolidated statements of operations | 7,674 | (11,395) |  |
Investments, Realized Gain (Loss) |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Net realized gain (loss) | 428 | 46 |  |
Investments, Unrealized Gain (Loss) |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Net realized gain (loss) | 6,984 | (11,395) |  |
First lien debt |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair value, beginning of period | 10,178,311 | 9,225,290 | 9,564,203 | 9,275,511
Purchases of investments | 734,974 | 114,229 |  |
Proceeds from principal repayments and sales of investments | (186,370) | (71,040) |  |
Accretion of discount/(amortization of premium) | 9,341 | 8,407 |  |
Transfers into Level 3 | 50,239 | 4,938 |  |
Transfers out of Level 3 | 0 | (91,939) |  |
Fair value, end of period | 10,178,311 | 9,225,290 |  |
Net change in unrealized appreciation (depreciation) included in earnings related to financial instruments, included in net unrealized appreciation (depreciation) on the consolidated statements of operations | 6,191 | (14,862) |  |
Debt Securities, First Lien, Realized Gain (Loss) |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Net realized gain (loss) | 428 | 46 |  |
Debt Securities, First Lien, Unrealized Gain (Loss) |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Net realized gain (loss) | 5,496 | (14,862) |  |
Second lien debt |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair value, beginning of period | 41,515 | 46,678 | 41,515 | 46,336
Purchases of investments | 180 | 411 |  |
Proceeds from principal repayments and sales of investments | 0 | 0 |  |
Accretion of discount/(amortization of premium) | 25 | 36 |  |
Transfers into Level 3 | 0 | 0 |  |
Transfers out of Level 3 | 0 | 0 |  |
Fair value, end of period | 41,515 | 46,678 |  |
Net change in unrealized appreciation (depreciation) included in earnings related to financial instruments, included in net unrealized appreciation (depreciation) on the consolidated statements of operations | (205) | (105) |  |
Debt Securities, Second Lien, Realized Gain (Loss) |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Net realized gain (loss) | 0 | 0 |  |
Debt Securities, Second Lien, Unrealized Gain (Loss) |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Net realized gain (loss) | (205) | (105) |  |
Unsecured debt |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair value, beginning of period | 11,859 |  | 9,924 |
Purchases of investments | 1,785 |  |  |
Proceeds from principal repayments and sales of investments | 0 |  |  |
Accretion of discount/(amortization of premium) | 9 |  |  |
Transfers into Level 3 | 0 |  |  |
Transfers out of Level 3 | 0 |  |  |
Fair value, end of period | 11,859 |  |  |
Net change in unrealized appreciation (depreciation) included in earnings related to financial instruments, included in net unrealized appreciation (depreciation) on the consolidated statements of operations | 135 |  |  |
Unsecured Debt, Realized Gain (Loss) |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Net realized gain (loss) | 0 |  |  |
Unsecured Debt, Unrealized Gain (Loss) |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Net realized gain (loss) | 141 |  |  |
Investments in equity |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Fair value, beginning of period | 98,680 | 154,521 | $ 94,940 | $ 150,949
Purchases of investments | 2,188 | 0 |  |
Proceeds from principal repayments and sales of investments | 0 | 0 |  |
Accretion of discount/(amortization of premium) | 0 | 0 |  |
Transfers into Level 3 | 0 | 0 |  |
Transfers out of Level 3 | 0 | 0 |  |
Fair value, end of period | 98,680 | 154,521 |  |
Net change in unrealized appreciation (depreciation) included in earnings related to financial instruments, included in net unrealized appreciation (depreciation) on the consolidated statements of operations | 1,553 | 3,572 |  |
Equity Securities, Realized Gain (Loss) |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Net realized gain (loss) | 0 | 0 |  |
Equity Securities, Unrealized Gain (Loss) |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Net realized gain (loss) | $ 1,552 | $ 3,572 |  |

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