Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended			12 Months Ended
		Mar. 31, 2025		Mar. 31, 2024	Mar. 31, 2025		Mar. 31, 2024	Sep. 30, 2024
Cash flows from operating activities
Net increase (decrease) in net assets resulting from operations		$ 78,984		$ 93,558	$ 190,298		$ 169,334
Adjustments to reconcile net increase (decrease) in net assets resulting from operations to net cash provided by (used in) operating activities:
Amortization of deferred debt issuance costs		2,479		2,546	5,124		4,655
Accretion of discounts and amortization of premiums on investments					(2,678)		(7,450)
Accretion of discounts and amortization of premiums on issued debt securities					1,681		455
Net realized (gain) loss on investments					42,220		17,368
Net realized (gain) loss on foreign currency transactions		174		(4,459)	3,879		(4,646)
Net realized (gain) loss on forward currency contracts		(5,997)		0	(7,203)		0
Net realized (gain) loss on extinguishment of debt		0		0	48		0
Net change in unrealized (appreciation) depreciation on investments					(38,906)		(17,013)
Net change in unrealized (appreciation) depreciation on translation of assets and liabilities in foreign currencies		(11,427)		10,156	11,546		3,969
Proceeds from (fundings of) revolving loans, net					(5,016)		(1,658)
Fundings of investments					(1,208,048)		(147,267)
Proceeds from principal payments and sales of portfolio investments					840,343		321,264
Proceeds from settlements of forward currency contracts					10,264		0
Payment-in-kind interest capitalized		(14,710)		(9,682)	(27,921)		(23,397)
Non-cash dividends capitalized					(15,071)		(8,603)
Proceeds from non-cash dividends					3,549		0
Changes in operating assets and liabilities:
Cash collateral held at broker for derivatives					0		(4,800)
Interest receivable					8,293		(4,027)
Receivable for investments sold					0		(3,727)
Other assets					385		283
Interest payable					4,772		11,840
Management and incentive fees payable					7,250		(6,106)
Accrued trustee fees					89		(94)
Accounts payable and other liabilities					(2,459)		8,479
Net cash provided by (used in) operating activities					(179,296)		313,014
Cash flows from financing activities
Borrowings on debt					3,731,443		1,145,606
Repayments of debt					(3,496,076)		(999,698)
Capitalized debt issuance costs					(5,995)		(13,343)
Net proceeds from issuance of common stock (Note 11)					37,434		0
Purchases of common stock (Note 11)					(1,130)		0
Distributions paid					(197,633)		(123,572)
Net cash provided by (used in) financing activities					68,043		8,993
Net change in cash and cash equivalents, foreign currencies, restricted cash and cash equivalents and restricted foreign currencies					(111,253)		322,007
Effect of foreign currency exchange rates					(1,915)		(1,865)
Cash and cash equivalents, foreign currencies, restricted cash and cash equivalents and restricted foreign currencies, beginning of period					359,552	[1]	140,206	$ 140,206
Cash and cash equivalents, foreign currencies, restricted cash and cash equivalents and restricted foreign currencies, end of period		246,384	[1]	460,348	246,384	[1]	460,348	359,552	[1]
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	[2]				133,282		71,205
Distributions declared for the period		231,337		153,092	231,337		153,092
Supplemental disclosure of non-cash financing activities:
Stock issued in connection with dividend reinvestment plan					33,704		29,520
Reconciliation of cash and cash equivalents, foreign currencies and restricted cash and cash equivalents and restricted foreign currencies
Cash and cash equivalents		103,136			103,136			123,120
Foreign currencies (cost of $13,763 and $7,973, respectively)		13,791			13,791			8,044
Restricted cash and cash equivalents		129,457			129,457			227,152
Restricted foreign currencies (cost of $0 and $1,219, respectively)		0			0			1,236
Total cash and cash equivalents, foreign currencies, restricted cash and cash equivalents and restricted foreign currencies shown in the Consolidated Statements of Cash Flows		246,384	[1]	460,348	246,384	[1]	460,348	$ 359,552	[1]
Interest Rate Swap
Adjustments to reconcile net increase (decrease) in net assets resulting from operations to net cash provided by (used in) operating activities:
Net change in unrealized (appreciation) depreciation on derivatives					4,697		2,772
Foreign exchange
Adjustments to reconcile net increase (decrease) in net assets resulting from operations to net cash provided by (used in) operating activities:
Net realized (gain) loss on forward currency contracts		(5,997)		0	(7,203)		0
Net change in unrealized (appreciation) depreciation on derivatives		$ 15,495		$ (4,332)	$ (6,432)		$ 1,383

[1] See Note 2 for a description of cash and cash equivalents, foreign currencies, restricted cash and cash equivalents and restricted foreign currencies.

[2] Includes cash paid or received for contractual interest rate swaps, which may have different contractual settlement dates among the (i) fixed interest leg, (ii) floating interest leg and (iii) the debt instrument.