Portfolio Investments - Schedule of Portfolio Composition (Details) - USD ($)
$ in Thousands |
9 Months Ended |
12 Months Ended |
Jun. 30, 2026 |
Sep. 30, 2025 |
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 2,996,697
|
$ 3,075,122
|
| Investments at fair value |
$ 2,741,814
|
$ 2,847,782
|
| Investment owned, percent of net assets (as a percent) |
198.24%
|
194.28%
|
| Northeast |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 1,128,846
|
$ 1,072,606
|
| Investments at fair value |
$ 998,676
|
$ 949,839
|
| Investment owned, percent of net assets (as a percent) |
72.20%
|
64.80%
|
| Midwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 432,203
|
$ 490,842
|
| Investments at fair value |
$ 420,250
|
$ 479,452
|
| Investment owned, percent of net assets (as a percent) |
30.39%
|
32.71%
|
| Southeast |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 370,908
|
$ 479,013
|
| Investments at fair value |
$ 298,299
|
$ 385,283
|
| Investment owned, percent of net assets (as a percent) |
21.57%
|
26.28%
|
| West |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 304,984
|
$ 284,586
|
| Investments at fair value |
$ 295,873
|
$ 283,930
|
| Investment owned, percent of net assets (as a percent) |
21.39%
|
19.37%
|
| International |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 292,413
|
$ 339,829
|
| Investments at fair value |
$ 294,476
|
$ 354,855
|
| Investment owned, percent of net assets (as a percent) |
21.29%
|
24.21%
|
| Southwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 246,076
|
$ 234,192
|
| Investments at fair value |
$ 213,779
|
$ 221,920
|
| Investment owned, percent of net assets (as a percent) |
15.46%
|
15.14%
|
| South |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 169,017
|
$ 164,434
|
| Investments at fair value |
$ 168,499
|
$ 162,946
|
| Investment owned, percent of net assets (as a percent) |
12.18%
|
11.12%
|
| Northwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 52,250
|
$ 9,620
|
| Investments at fair value |
$ 51,962
|
$ 9,557
|
| Investment owned, percent of net assets (as a percent) |
3.76%
|
0.65%
|
| Investment Owned, At Cost | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
100.00%
|
100.00%
|
| Investment Owned, At Cost | Geographic Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
100.00%
|
100.00%
|
| Investment Owned, At Cost | Geographic Concentration Risk | Northeast |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
37.67%
|
34.88%
|
| Investment Owned, At Cost | Geographic Concentration Risk | Midwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
14.42%
|
15.96%
|
| Investment Owned, At Cost | Geographic Concentration Risk | Southeast |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
12.38%
|
15.58%
|
| Investment Owned, At Cost | Geographic Concentration Risk | West |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
10.18%
|
9.25%
|
| Investment Owned, At Cost | Geographic Concentration Risk | International |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
9.76%
|
11.05%
|
| Investment Owned, At Cost | Geographic Concentration Risk | Southwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
8.21%
|
7.62%
|
| Investment Owned, At Cost | Geographic Concentration Risk | South |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
5.64%
|
5.35%
|
| Investment Owned, At Cost | Geographic Concentration Risk | Northwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
1.74%
|
0.31%
|
| Investment Owned, At Fair Value | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
100.00%
|
100.00%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
100.00%
|
100.00%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | Northeast |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
36.41%
|
33.35%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | Midwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
15.33%
|
16.84%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | Southeast |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
10.88%
|
13.53%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | West |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
10.79%
|
9.97%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | International |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
10.74%
|
12.46%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | Southwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
7.80%
|
7.79%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | South |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
6.15%
|
5.72%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | Northwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
1.90%
|
0.34%
|
| Senior secured debt |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 2,425,385
|
$ 2,555,861
|
| Investments at fair value |
$ 2,316,840
|
$ 2,445,538
|
| Investment owned, percent of net assets (as a percent) |
167.51%
|
166.84%
|
| Senior secured debt | Investment Owned, At Cost | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
80.93%
|
83.11%
|
| Senior secured debt | Investment Owned, At Fair Value | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
84.50%
|
85.88%
|
| Subordinated debt |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 163,875
|
$ 90,962
|
| Investments at fair value |
$ 162,682
|
$ 90,460
|
| Investment owned, percent of net assets (as a percent) |
11.76%
|
6.17%
|
| Subordinated debt | Investment Owned, At Cost | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
5.47%
|
2.96%
|
| Subordinated debt | Investment Owned, At Fair Value | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
5.93%
|
3.18%
|
| Debt investments in the JVs |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 138,778
|
$ 165,779
|
| Investments at fair value |
$ 125,828
|
$ 158,716
|
| Investment owned, percent of net assets (as a percent) |
9.10%
|
10.83%
|
| Debt investments in the JVs | Investment Owned, At Cost | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
4.63%
|
5.39%
|
| Debt investments in the JVs | Investment Owned, At Fair Value | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
4.59%
|
5.57%
|
| Common equity and warrants |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 134,523
|
$ 139,256
|
| Investments at fair value |
$ 58,870
|
$ 69,000
|
| Investment owned, percent of net assets (as a percent) |
4.26%
|
4.71%
|
| Common equity and warrants | Investment Owned, At Cost | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
4.49%
|
4.53%
|
| Common equity and warrants | Investment Owned, At Fair Value | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
2.15%
|
2.42%
|
| LLC equity interests of the JVs |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 82,957
|
$ 54,791
|
| Investments at fair value |
$ 28,728
|
$ 11,946
|
| Investment owned, percent of net assets (as a percent) |
2.08%
|
0.81%
|
| LLC equity interests of the JVs | Investment Owned, At Cost | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
2.77%
|
1.78%
|
| LLC equity interests of the JVs | Investment Owned, At Fair Value | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
1.05%
|
0.42%
|
| Preferred equity |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 51,179
|
$ 68,473
|
| Investments at fair value |
$ 48,866
|
$ 72,122
|
| Investment owned, percent of net assets (as a percent) |
3.53%
|
4.92%
|
| Preferred equity | Investment Owned, At Cost | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
1.71%
|
2.23%
|
| Preferred equity | Investment Owned, At Fair Value | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
1.78%
|
2.53%
|