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, 2025 |
Sep. 30, 2024 |
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 8,967,518
|
|
$ 8,302,913
|
|
| Fair Value |
$ 8,961,549
|
[1] |
$ 8,235,411
|
[2] |
| Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
100.00%
|
|
100.00%
|
|
| Amortized Cost | Industry Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
100.00%
|
|
100.00%
|
|
| Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
100.00%
|
|
100.00%
|
|
| Fair Value | Industry Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
100.00%
|
|
100.00%
|
|
| Mid-Atlantic |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 1,577,535
|
|
$ 1,502,136
|
|
| Fair Value |
$ 1,598,556
|
|
$ 1,506,726
|
|
| Mid-Atlantic | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
17.60%
|
|
18.10%
|
|
| Mid-Atlantic | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
17.80%
|
|
18.30%
|
|
| Midwest |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 1,388,979
|
|
$ 1,391,538
|
|
| Fair Value |
$ 1,395,298
|
|
$ 1,352,353
|
|
| Midwest | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
15.50%
|
|
16.80%
|
|
| Midwest | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
15.60%
|
|
16.40%
|
|
| West |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 1,352,377
|
|
$ 1,133,878
|
|
| Fair Value |
$ 1,355,968
|
|
$ 1,130,497
|
|
| West | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
15.10%
|
|
13.70%
|
|
| West | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
15.10%
|
|
13.70%
|
|
| Southeast |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 1,794,992
|
|
$ 1,638,221
|
|
| Fair Value |
$ 1,750,634
|
|
$ 1,634,599
|
|
| Southeast | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
20.00%
|
|
19.70%
|
|
| Southeast | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
19.50%
|
|
19.80%
|
|
| Southwest |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 1,144,848
|
|
$ 1,041,814
|
|
| Fair Value |
$ 1,120,584
|
|
$ 1,020,950
|
|
| Southwest | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
12.80%
|
|
12.50%
|
|
| Southwest | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
12.50%
|
|
12.40%
|
|
| Northeast |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 570,645
|
|
$ 713,024
|
|
| Fair Value |
$ 571,480
|
|
$ 713,123
|
|
| Northeast | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
6.40%
|
|
8.60%
|
|
| Northeast | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
6.40%
|
|
8.70%
|
|
| Canada |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 374,296
|
|
$ 182,002
|
|
| Fair Value |
$ 370,838
|
|
$ 178,003
|
|
| Canada | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
4.20%
|
|
2.20%
|
|
| Canada | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
4.10%
|
|
2.20%
|
|
| United Kingdom |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 390,652
|
|
$ 395,769
|
|
| Fair Value |
$ 402,492
|
|
$ 395,840
|
|
| United Kingdom | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
4.40%
|
|
4.80%
|
|
| United Kingdom | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
4.50%
|
|
4.80%
|
|
| Australia |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 54,195
|
|
$ 20,909
|
|
| Fair Value |
$ 53,257
|
|
$ 20,113
|
|
| Australia | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.60%
|
|
0.20%
|
|
| Australia | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.60%
|
|
0.20%
|
|
| Luxembourg |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 4,566
|
|
$ 58,328
|
|
| Fair Value |
$ 4,882
|
|
$ 57,439
|
|
| Luxembourg | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.00%
|
|
0.70%
|
|
| Luxembourg | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.10%
|
|
0.70%
|
|
| Netherlands |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 12,824
|
|
$ 95,950
|
|
| Fair Value |
$ 13,226
|
|
$ 89,708
|
|
| Netherlands | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.10%
|
|
1.20%
|
|
| Netherlands | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.10%
|
|
1.10%
|
|
| Finland |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 78,915
|
|
$ 52,670
|
|
| Fair Value |
$ 88,369
|
|
$ 56,608
|
|
| Finland | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.90%
|
|
0.60%
|
|
| Finland | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
1.00%
|
|
0.70%
|
|
| Sweden |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 34,681
|
|
$ 33,243
|
|
| Fair Value |
$ 36,891
|
|
$ 34,709
|
|
| Sweden | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.40%
|
|
0.40%
|
|
| Sweden | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.40%
|
|
0.40%
|
|
| Israel |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 17,381
|
|
$ 855
|
|
| Fair Value |
$ 17,665
|
|
$ 1,008
|
|
| Israel | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.20%
|
|
0.00%
|
|
| Israel | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.20%
|
|
0.00%
|
|
| Denmark |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 4,865
|
|
$ 4,860
|
|
| Fair Value |
$ 4,843
|
|
$ 4,896
|
|
| Denmark | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.00%
|
|
0.10%
|
|
| Denmark | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.10%
|
|
0.10%
|
|
| Germany |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 79,107
|
|
$ 19,896
|
|
| Fair Value |
$ 85,152
|
|
$ 20,493
|
|
| Germany | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.90%
|
|
0.20%
|
|
| Germany | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
1.00%
|
|
0.30%
|
|
| France |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 20,238
|
|
$ 17,820
|
|
| Fair Value |
$ 22,204
|
|
$ 18,346
|
|
| France | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.20%
|
|
0.20%
|
|
| France | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.20%
|
|
0.20%
|
|
| Jersey |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 57,476
|
|
$ 0
|
|
| Fair Value |
$ 60,125
|
|
$ 0
|
|
| Jersey | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.60%
|
|
0.00%
|
|
| Jersey | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.70%
|
|
0.00%
|
|
| Spain |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Amortized Cost |
$ 8,946
|
|
$ 0
|
|
| Fair Value |
$ 9,085
|
|
$ 0
|
|
| Spain | Amortized Cost | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.10%
|
|
0.00%
|
|
| Spain | Fair Value | Geographic Concentration Risk |
|
|
|
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
|
|
|
|
| Concentration risk, percentage |
0.10%
|
|
0.00%
|
|
|
|