Portfolio Investments - Schedule of Financial Instruments Carried at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2023		Sep. 30, 2023
Schedule of Investments [Line Items]
Investments at fair value	$ 2,857,808	[1]	$ 1,927,237	[2]
Derivative asset	10,566		2,041
Total assets at fair value	2,868,374		1,929,278
Derivative liabilities	2,817		0
Total liabilities at fair value	2,817
Senior secured debt
Schedule of Investments [Line Items]
Investments at fair value	2,659,602		1,817,981
Subordinated Debt
Schedule of Investments [Line Items]
Investments at fair value	181,043		97,616
Preferred Equity
Schedule of Investments [Line Items]
Investments at fair value	12,091		5,748
Common Equity and Warrants
Schedule of Investments [Line Items]
Investments at fair value	5,072		5,892
Level 1
Schedule of Investments [Line Items]
Investments at fair value	0		0
Derivative asset	0		0
Total assets at fair value	0		0
Derivative liabilities	0
Total liabilities at fair value	0
Level 1 | Senior secured debt
Schedule of Investments [Line Items]
Investments at fair value	0		0
Level 1 | Subordinated Debt
Schedule of Investments [Line Items]
Investments at fair value	0		0
Level 1 | Preferred Equity
Schedule of Investments [Line Items]
Investments at fair value	0		0
Level 1 | Common Equity and Warrants
Schedule of Investments [Line Items]
Investments at fair value	0		0
Level 2
Schedule of Investments [Line Items]
Investments at fair value	1,194,065		838,097
Derivative asset	10,566		2,041
Total assets at fair value	1,204,631		840,138
Derivative liabilities	2,817
Total liabilities at fair value	2,817
Level 2 | Senior secured debt
Schedule of Investments [Line Items]
Investments at fair value	1,038,374		754,220
Level 2 | Subordinated Debt
Schedule of Investments [Line Items]
Investments at fair value	155,691		83,824
Level 2 | Preferred Equity
Schedule of Investments [Line Items]
Investments at fair value	0		0
Level 2 | Common Equity and Warrants
Schedule of Investments [Line Items]
Investments at fair value	0		53
Level 3
Schedule of Investments [Line Items]
Investments at fair value	1,663,743		1,089,140
Derivative asset	0		0
Total assets at fair value	1,663,743		1,089,140
Derivative liabilities	0
Total liabilities at fair value	0
Level 3 | Senior secured debt
Schedule of Investments [Line Items]
Investments at fair value	1,621,228		1,063,761
Level 3 | Subordinated Debt
Schedule of Investments [Line Items]
Investments at fair value	25,352		13,792
Level 3 | Preferred Equity
Schedule of Investments [Line Items]
Investments at fair value	12,091		5,748
Level 3 | Common Equity and Warrants
Schedule of Investments [Line Items]
Investments at fair value	$ 5,072		$ 5,839

[1] Non-Control/Non-Affiliate Investments are investments that are neither Control Investments nor Affiliate Investments. Control Investments generally are defined by the Investment Company Act of 1940, as amended (the "Investment Company Act"), as investments in companies in which the Company owns more than 25% of the voting securities and/or has the power to exercise control over the management or policies of the company. Affiliate Investments generally are defined by the Investment Company Act as investments in companies in which the Company owns between 5% and 25% of the voting securities.

[2] Non-Control/Non-Affiliate Investments are investments that are neither Control Investments nor Affiliate Investments. Control Investments generally are defined by the Investment Company Act of 1940, as amended (the "Investment Company Act"), as investments in companies in which the Company owns more than 25% of the voting securities and/or has the power to exercise control over the management or policies of the company. Affiliate Investments generally are defined by the Investment Company Act as investments in companies in which the Company owns between 5% and 25% of the voting securities.