Investments - Schedule of Composition of the Company's Investment Portfolio by Geographic Region, 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 | Geographic Concentration Risk

Investments

Concentration risk, percentage

100.00%

100.00%

Investment Owned, At Fair Value | Geographic Concentration Risk

Investments

Concentration risk, percentage

100.00%

100.00%

Investments

$ 1,081,929

$ 1,093,220

$ 988,682

$ 1,007,605

Midwest | Investment Owned, At Cost | Geographic Concentration Risk

Investments

Concentration risk, percentage

18.30%

18.50%

Midwest | Investment Owned, At Fair Value | Geographic Concentration Risk

Investments

Concentration risk, percentage

17.10%

17.30%

Investments

$ 1,319,510

$ 1,337,031

$ 1,325,343

$ 1,345,901

Northeast | Investment Owned, At Cost | Geographic Concentration Risk

Investments

Concentration risk, percentage

22.30%

22.60%

Northeast | Investment Owned, At Fair Value | Geographic Concentration Risk

Investments

Concentration risk, percentage

22.80%

23.10%

Investments

$ 75,666

$ 106,019

$ 75,927

$ 108,809

Northwest | Investment Owned, At Cost | Geographic Concentration Risk

Investments

Concentration risk, percentage

1.30%

1.80%

Northwest | Investment Owned, At Fair Value | Geographic Concentration Risk

Investments

Concentration risk, percentage

1.30%

1.90%

Investments

$ 1,509,315

$ 1,431,430

$ 1,549,169

$ 1,471,723

Southeast | Investment Owned, At Cost | Geographic Concentration Risk

Investments

Concentration risk, percentage

25.50%

24.20%

Southeast | Investment Owned, At Fair Value | Geographic Concentration Risk

Investments

Concentration risk, percentage

26.70%

25.30%

Investments

$ 610,811

$ 602,184

$ 587,555

$ 578,702

Southwest | Investment Owned, At Cost | Geographic Concentration Risk

Investments

Concentration risk, percentage

10.40%

10.20%

Southwest | Investment Owned, At Fair Value | Geographic Concentration Risk

Investments

Concentration risk, percentage

10.10%

9.90%

Investments

$ 1,071,815

$ 1,075,499

$ 1,031,465

$ 1,044,597

West | Investment Owned, At Cost | Geographic Concentration Risk

Investments

Concentration risk, percentage

18.20%

18.30%

West | Investment Owned, At Fair Value | Geographic Concentration Risk

Investments

Concentration risk, percentage

17.80%

18.00%

Investments

$ 247,227

$ 267,980

$ 246,416

$ 262,418

International | Investment Owned, At Cost | Geographic Concentration Risk

Investments

Concentration risk, percentage

4.00%

4.40%

International | Investment Owned, At Fair Value | Geographic Concentration Risk

Investments

Concentration risk, percentage

4.20%

4.50%

[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).