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Fair Value Measurements - Summary of Changes in Fair Value of Investments Measured Using Level 3 Inputs (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
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 | $ 9,472,796 | $ 9,501,329
Purchases of investments | 1,508,759 | 952,854
Proceeds from principal repayments and sales of investments | (1,187,790) | (1,042,362)
Accretion of discount/amortization of premium | 50,580 | 45,270
Transfers into Level 3 | 4,938 | 108,674
Transfers out of Level 3 | (91,939) | 0
Fair value, end of period | 9,710,582 | 9,472,796
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 | (44,082) | (97,281)
Investments, Realized Gain (Loss) |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Net realized gain (loss) | (1,662) | 39,361
Investments, Unrealized Gain (Loss) |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Net realized gain (loss) | (45,100) | (132,330)
First lien debt |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Fair value, beginning of period | 9,275,511 | 9,288,184
Purchases of investments | 1,492,985 | 934,505
Proceeds from principal repayments and sales of investments | (1,114,974) | (980,395)
Accretion of discount/amortization of premium | 50,516 | 45,133
Transfers into Level 3 | 4,938 | 108,674
Transfers out of Level 3 | (91,939) | 0
Fair value, end of period | 9,564,203 | 9,275,511
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 | (38,013) | (119,180)
Debt Securities, First Lien, Realized Gain (Loss) |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Net realized gain (loss) | (15,095) | (2,125)
Debt Securities, First Lien, Unrealized Gain (Loss) |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Net realized gain (loss) | (37,739) | (118,465)
Second lien debt |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Fair value, beginning of period | 46,336 | 42,880
Purchases of investments | 1,935 | 5,949
Proceeds from principal repayments and sales of investments | (7,351) | 0
Accretion of discount/amortization of premium | 58 | 137
Transfers into Level 3 | 0 | 0
Transfers out of Level 3 | 0 | 0
Fair value, end of period | 41,515 | 46,336
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 | 374 | (2,629)
Debt Securities, Second Lien, Realized Gain (Loss) |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Net realized gain (loss) | (49) | 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) | 586 | (2,630)
Unsecured debt |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Fair value, beginning of period | 0 |
Purchases of investments | 9,924 |
Proceeds from principal repayments and sales of investments | 0 |
Accretion of discount/amortization of premium | 6 |
Transfers into Level 3 | 0 |
Transfers out of Level 3 | 0 |
Fair value, end of period | 9,924 | 0
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) |
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) | (6) |
Investments in equity |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Fair value, beginning of period | 150,949 | 170,265
Purchases of investments | 3,915 | 12,400
Proceeds from principal repayments and sales of investments | (65,465) | (61,967)
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 | 94,940 | 150,949
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 | (6,437) | 24,528
Equity Securities, Realized Gain (Loss) |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Net realized gain (loss) | 13,482 | 41,486
Equity Securities, Unrealized Gain (Loss) |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Net realized gain (loss) | $ (7,941) | $ (11,235)

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