Investments - Schedules of Portfolio Composition by Geographic Region at Amortization Cost and Fair Value (Details) - USD ($)
$ in Thousands |
9 Months Ended |
12 Months Ended |
Jun. 30, 2026 |
Sep. 30, 2025 |
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 9,727,658
|
|
$ 8,479,341
|
|
| Fair Value |
$ 9,616,525
|
[1] |
$ 8,555,251
|
[2] |
| Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
100.00%
|
|
100.00%
|
|
| Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
100.00%
|
|
100.00%
|
|
| Southeast |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 1,892,252
|
|
$ 1,698,394
|
|
| Fair Value |
$ 1,874,381
|
|
$ 1,704,931
|
|
| Southeast | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
19.50%
|
|
20.00%
|
|
| Southeast | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
19.50%
|
|
19.90%
|
|
| Midwest |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 1,613,425
|
|
$ 1,445,453
|
|
| Fair Value |
$ 1,594,650
|
|
$ 1,447,480
|
|
| Midwest | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
16.60%
|
|
17.00%
|
|
| Midwest | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
16.60%
|
|
16.90%
|
|
| Mid-Atlantic |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 1,579,538
|
|
$ 1,208,533
|
|
| Fair Value |
$ 1,565,311
|
|
$ 1,215,555
|
|
| Mid-Atlantic | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
16.20%
|
|
14.30%
|
|
| Mid-Atlantic | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
16.30%
|
|
14.20%
|
|
| West |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 1,472,920
|
|
$ 1,159,934
|
|
| Fair Value |
$ 1,442,774
|
|
$ 1,163,587
|
|
| West | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
15.20%
|
|
13.70%
|
|
| West | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
15.00%
|
|
13.60%
|
|
| Southwest |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 1,139,686
|
|
$ 1,050,633
|
|
| Fair Value |
$ 1,131,453
|
|
$ 1,060,849
|
|
| Southwest | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
11.70%
|
|
12.40%
|
|
| Southwest | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
11.80%
|
|
12.40%
|
|
| Northeast |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 344,059
|
|
$ 395,788
|
|
| Fair Value |
$ 330,725
|
|
$ 397,933
|
|
| Northeast | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
3.50%
|
|
4.70%
|
|
| Northeast | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
3.40%
|
|
4.70%
|
|
| U.S. Territory |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 498
|
|
$ 12,399
|
|
| Fair Value |
$ 501
|
|
$ 12,497
|
|
| U.S. Territory | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.00%
|
|
0.10%
|
|
| U.S. Territory | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.00%
|
|
0.10%
|
|
| United Kingdom |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 765,446
|
|
$ 676,804
|
|
| Fair Value |
$ 753,588
|
|
$ 686,479
|
|
| United Kingdom | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
7.90%
|
|
8.00%
|
|
| United Kingdom | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
7.80%
|
|
8.00%
|
|
| Germany |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 206,715
|
|
$ 241,578
|
|
| Fair Value |
$ 207,810
|
|
$ 260,620
|
|
| Germany | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
2.10%
|
|
2.80%
|
|
| Germany | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
2.20%
|
|
3.00%
|
|
| Cayman Islands |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 178,285
|
|
$ 140,879
|
|
| Fair Value |
$ 176,197
|
|
$ 142,238
|
|
| Cayman Islands | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
1.80%
|
|
1.70%
|
|
| Cayman Islands | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
1.80%
|
|
1.70%
|
|
| Australia |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 166,523
|
|
$ 162,334
|
|
| Fair Value |
$ 174,064
|
|
$ 166,823
|
|
| Australia | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
1.70%
|
|
2.00%
|
|
| Australia | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
1.80%
|
|
2.00%
|
|
| Canada |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 138,735
|
|
$ 101,412
|
|
| Fair Value |
$ 134,624
|
|
$ 101,943
|
|
| Canada | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
1.40%
|
|
1.20%
|
|
| Canada | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
1.40%
|
|
1.20%
|
|
| Jersey |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 101,876
|
|
$ 88,930
|
|
| Fair Value |
$ 101,888
|
|
$ 91,593
|
|
| Jersey | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
1.10%
|
|
1.00%
|
|
| Jersey | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
1.10%
|
|
1.10%
|
|
| Finland |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 41,900
|
|
$ 36,394
|
|
| Fair Value |
$ 42,424
|
|
$ 39,388
|
|
| Finland | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.40%
|
|
0.40%
|
|
| Finland | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.40%
|
|
0.50%
|
|
| France |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 38,960
|
|
$ 18,800
|
|
| Fair Value |
$ 39,091
|
|
$ 20,597
|
|
| France | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.40%
|
|
0.20%
|
|
| France | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.40%
|
|
0.20%
|
|
| Netherlands |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 27,142
|
|
$ 27,046
|
|
| Fair Value |
$ 27,388
|
|
$ 28,309
|
|
| Netherlands | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.30%
|
|
0.30%
|
|
| Netherlands | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.30%
|
|
0.30%
|
|
| Luxembourg |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 5,667
|
|
$ 5,505
|
|
| Fair Value |
$ 5,137
|
|
$ 5,839
|
|
| Luxembourg | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.10%
|
|
0.10%
|
|
| Luxembourg | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.10%
|
|
0.10%
|
|
| Israel |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 12,031
|
|
$ 0
|
|
| Fair Value |
$ 12,562
|
|
$ 0
|
|
| Israel | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.10%
|
|
0.00%
|
|
| Israel | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.10%
|
|
0.00%
|
|
| Sweden |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 2,000
|
|
$ 0
|
|
| Fair Value |
$ 1,957
|
|
$ 0
|
|
| Sweden | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.00%
|
|
0.00%
|
|
| Sweden | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.00%
|
|
0.00%
|
|
| Lithuania |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 0
|
|
$ 6,965
|
|
| Fair Value |
$ 0
|
|
$ 7,004
|
|
| Lithuania | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.00%
|
|
0.10%
|
|
| Lithuania | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.00%
|
|
0.10%
|
|
| Spain |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Amortized Cost |
$ 0
|
|
$ 1,560
|
|
| Fair Value |
$ 0
|
|
$ 1,586
|
|
| Spain | Investments, at Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.00%
|
|
0.00%
|
|
| Spain | Investments, at Fair Value | Geographic Concentration Risk |
|
|
|
|
| Schedule of Investments [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.00%
|
|
0.00%
|
|
|
|