Investments - Schedule of Composition of the Company's Investment Portfolio, at Amortized Cost and Fair Value (with Corresponding Percentage of Total Portfolio Investments) (Details) - USD ($)
$ in Thousands

3 Months Ended

12 Months Ended

Mar. 31, 2026

Dec. 31, 2025

Investments

$ 5,916,273

^[1]

$ 5,913,363

^[2]

$ 5,804,557

^[1],[3]

$ 5,819,755

^[2],[4]

Concentration risk, percentage

100.00%

Investment Owned, At Cost | Investment Type Concentration Risk

Investments

Concentration risk, percentage

100.00%

100.00%

Investment Owned, At Fair Value | Investment Type Concentration Risk

Investments

Concentration risk, percentage

100.00%

100.00%

Senior secured loans

Investments

$ 5,053,789

$ 5,109,431

$ 5,029,403

$ 5,090,861

Senior secured loans | Investment Owned, At Cost | Investment Type Concentration Risk

Investments

Concentration risk, percentage

85.40%

86.40%

Senior secured loans | Investment Owned, At Fair Value | Investment Type Concentration Risk

Investments

Concentration risk, percentage

86.60%

87.40%

Unitranche secured loans

Investments

$ 18,117

$ 35,221

$ 18,159

$ 35,414

Unitranche secured loans | Investment Owned, At Cost | Investment Type Concentration Risk

Investments

Concentration risk, percentage

0.30%

0.60%

Unitranche secured loans | Investment Owned, At Fair Value | Investment Type Concentration Risk

Investments

Concentration risk, percentage

0.30%

0.60%

Junior secured loans

Investments

$ 409,020

$ 361,428

$ 320,109

$ 277,025

Junior secured loans | Investment Owned, At Cost | Investment Type Concentration Risk

Investments

Concentration risk, percentage

6.90%

6.10%

Junior secured loans | Investment Owned, At Fair Value | Investment Type Concentration Risk

Investments

Concentration risk, percentage

5.60%

4.80%

Equity investments

Investments

$ 435,347

$ 407,283

$ 436,886

$ 416,455

Equity investments | Investment Owned, At Cost | Investment Type Concentration Risk

Investments

Concentration risk, percentage

7.40%

6.90%

Equity investments | Investment Owned, At Fair Value | Investment Type Concentration Risk

Investments

Concentration risk, percentage

7.50%

7.20%

[1]	All of the Company’s investments are issued by eligible portfolio companies, as defined in the Investment Company Act of 1940, as amended, (the “1940 Act”), unless otherwise noted. All of the Company’s investments are issued by U.S. portfolio companies unless otherwise noted.
[2]	All of the Company’s investments are issued by eligible portfolio companies, as defined in the Investment Company Act of 1940, as amended, (the “1940 Act”), unless otherwise noted. All of the Company’s investments are issued by U.S. portfolio companies unless otherwise noted.
[3]	Except as otherwise noted, because there is no readily available market value for these investments, the fair value of each of these investments is determined in good faith using significant unobservable inputs by the Valuation Designee (see Note 4 in the accompanying notes to the consolidated financial statements).
[4]	Except as otherwise noted, because there is no readily available market value for these investments, the fair value of each of these investments is determined in good faith using significant unobservable inputs by the Valuation Designee (see Note 4 in the accompanying notes to the consolidated financial statements).