Portfolio Investments - Schedule of Portfolio Composition (Details) - USD ($)
$ in Thousands |
9 Months Ended |
12 Months Ended |
Jun. 30, 2025 |
Sep. 30, 2024 |
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 3,012,589
|
$ 3,144,919
|
| Investments at fair value |
$ 2,809,377
|
$ 3,021,279
|
| Investment owned, percent of net assets (as a percent) |
190.28%
|
203.07%
|
| Northeast |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 1,005,796
|
$ 1,033,467
|
| Investments at fair value |
$ 891,015
|
$ 965,469
|
| Investment owned, percent of net assets (as a percent) |
60.34%
|
64.89%
|
| Midwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 498,752
|
$ 397,640
|
| Investments at fair value |
$ 489,418
|
$ 390,607
|
| Investment owned, percent of net assets (as a percent) |
33.15%
|
26.25%
|
| Southeast |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 471,215
|
$ 464,992
|
| Investments at fair value |
$ 380,023
|
$ 419,669
|
| Investment owned, percent of net assets (as a percent) |
25.74%
|
28.21%
|
| International |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 329,690
|
$ 343,033
|
| Investments at fair value |
$ 344,568
|
$ 354,662
|
| Investment owned, percent of net assets (as a percent) |
23.34%
|
23.84%
|
| West |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 310,077
|
$ 320,407
|
| Investments at fair value |
$ 321,504
|
$ 314,994
|
| Investment owned, percent of net assets (as a percent) |
21.78%
|
21.17%
|
| Southwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 217,930
|
$ 285,648
|
| Investments at fair value |
$ 207,486
|
$ 279,653
|
| Investment owned, percent of net assets (as a percent) |
14.05%
|
18.80%
|
| South |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 179,129
|
$ 241,098
|
| Investments at fair value |
$ 175,363
|
$ 237,634
|
| Investment owned, percent of net assets (as a percent) |
11.88%
|
15.97%
|
| Northwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 0
|
$ 58,634
|
| Investments at fair value |
$ 0
|
$ 58,591
|
| Investment owned, percent of net assets (as a percent) |
0.00%
|
3.94%
|
| 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) |
33.39%
|
32.86%
|
| Investment Owned, At Cost | Geographic Concentration Risk | Midwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
16.56%
|
12.64%
|
| Investment Owned, At Cost | Geographic Concentration Risk | Southeast |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
15.64%
|
14.79%
|
| Investment Owned, At Cost | Geographic Concentration Risk | International |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
10.94%
|
10.91%
|
| Investment Owned, At Cost | Geographic Concentration Risk | West |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
10.29%
|
10.19%
|
| Investment Owned, At Cost | Geographic Concentration Risk | Southwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
7.23%
|
9.08%
|
| Investment Owned, At Cost | Geographic Concentration Risk | South |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
5.95%
|
7.67%
|
| Investment Owned, At Cost | Geographic Concentration Risk | Northwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
0.00%
|
1.86%
|
| Investment Owned, At Fair Value |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investments at fair value |
$ 2,809,377
|
$ 3,021,279
|
| Investment owned, percent of net assets (as a percent) |
190.28%
|
203.07%
|
| 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) |
31.72%
|
31.94%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | Midwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
17.42%
|
12.93%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | Southeast |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
13.53%
|
13.89%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | International |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
12.26%
|
11.74%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | West |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
11.44%
|
10.43%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | Southwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
7.39%
|
9.26%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | South |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
6.24%
|
7.87%
|
| Investment Owned, At Fair Value | Geographic Concentration Risk | Northwest |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
0.00%
|
1.94%
|
| Senior secured debt |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 2,445,232
|
$ 2,615,066
|
| Investments at fair value |
$ 2,343,411
|
$ 2,574,937
|
| Investment owned, percent of net assets (as a percent) |
158.72%
|
173.06%
|
| Senior secured debt | Investment Owned, At Cost | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
81.17%
|
83.14%
|
| Senior secured debt | Investment Owned, At Fair Value | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
83.40%
|
85.21%
|
| Debt investments in the JVs |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 165,389
|
$ 164,324
|
| Investments at fair value |
$ 159,720
|
$ 161,552
|
| Investment owned, percent of net assets (as a percent) |
10.82%
|
10.86%
|
| Debt investments in the JVs | Investment Owned, At Cost | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
5.49%
|
5.23%
|
| Debt investments in the JVs | Investment Owned, At Fair Value | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
5.69%
|
5.35%
|
| Common equity and warrants |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 140,320
|
$ 134,452
|
| Investments at fair value |
$ 80,011
|
$ 86,008
|
| Investment owned, percent of net assets (as a percent) |
5.42%
|
5.78%
|
| Common equity and warrants | Investment Owned, At Cost | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
4.66%
|
4.28%
|
| Common equity and warrants | Investment Owned, At Fair Value | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
2.85%
|
2.85%
|
| Subordinated debt |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 138,724
|
$ 108,068
|
| Investments at fair value |
$ 138,122
|
$ 109,921
|
| Investment owned, percent of net assets (as a percent) |
9.35%
|
7.39%
|
| Subordinated debt | Investment Owned, At Cost | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
4.60%
|
3.44%
|
| Subordinated debt | Investment Owned, At Fair Value | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
4.92%
|
3.64%
|
| Preferred equity |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 68,133
|
$ 68,218
|
| Investments at fair value |
$ 73,232
|
$ 66,320
|
| Investment owned, percent of net assets (as a percent) |
4.96%
|
4.46%
|
| Preferred equity | Investment Owned, At Cost | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
2.26%
|
2.17%
|
| Preferred equity | Investment Owned, At Fair Value | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
2.61%
|
2.20%
|
| LLC equity interests of the JVs |
|
|
| Schedule of Investments [Line Items] |
|
|
| Investment owned, at cost |
$ 54,791
|
$ 54,791
|
| Investments at fair value |
$ 14,881
|
$ 22,541
|
| Investment owned, percent of net assets (as a percent) |
1.01%
|
1.52%
|
| LLC equity interests of the JVs | Investment Owned, At Cost | Investment Type Concentration Risk |
|
|
| Schedule of Investments [Line Items] |
|
|
| Concentration risk (as a percent) |
1.82%
|
1.74%
|
| 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) |
0.53%
|
0.75%
|