Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended			12 Months Ended
		Mar. 31, 2026		Mar. 31, 2025	Mar. 31, 2026		Mar. 31, 2025	Sep. 30, 2025
Cash flows from operating activities
Net increase (decrease) in net assets resulting from operations		$ (46,796)		$ 78,984	$ 18,450		$ 190,298
Adjustments to reconcile net increase (decrease) in net assets resulting from operations to net cash provided by (used in) operating activities:
Amortization of debt issuance costs		2,572		2,479	5,179		5,124
Accretion of discounts and amortization of premiums on investments					(6,596)		(2,678)
Accretion of discounts and amortization of premiums on issued debt securities					(563)		1,681
Net realized (gain) loss on investments					4,169		42,220
Net realized (gain) loss on foreign currency transactions		(1,354)		174	(234)		3,879
Net realized (gain) loss on forward currency contracts		10,258		(5,997)	10,258		(7,203)
Net realized (gain) loss on extinguishment of debt		0		0	0		48
Net change in unrealized (appreciation) depreciation on investments					160,646		(38,906)
Net change in unrealized (appreciation) depreciation on translation of assets and liabilities in foreign currencies		4,398		(11,427)	2,350		11,546
Proceeds from (fundings of) revolving loans, net					(11,314)		(5,016)
Fundings of investments					(296,134)		(1,208,048)
Proceeds from principal payments and sales of portfolio investments					639,511		840,343
Proceeds from settlements of forward currency contracts					(10,258)		10,264
Payment-in-kind interest capitalized		(18,561)		(14,710)	(32,718)		(27,921)
Non-cash dividends capitalized					(13,192)		(15,071)
Proceeds from non-cash dividends					235		3,549
Changes in operating assets and liabilities:
Interest receivable					4,353		8,293
Receivable for investments					3,686		0
Other assets					7,949		385
Interest payable					(4,363)		4,772
Management and income incentive fees payable					(4,351)		7,250
Accrued trustee fees					(393)		89
Accounts payable and other liabilities					(1,730)		(2,459)
Net cash provided by (used in) operating activities					460,777		(179,296)
Cash flows from financing activities
Borrowings on debt					378,068		3,731,443
Repayments of debt					(562,534)		(3,496,076)
Capitalized debt issuance costs					(601)		(5,995)
Net proceeds from issuance of common stock (Note 11)					0		37,434
Purchases of common stock (Note 11)					(63,708)		(1,130)
Distributions paid					(156,810)		(197,633)
Purchases of common stock for dividend reinvestment plan					(32,379)		0
Net cash provided by (used in) financing activities					(437,964)		68,043
Net change in cash, cash equivalents, foreign currencies, restricted cash, restricted cash equivalents and restricted foreign currencies					22,813		(111,253)
Effect of foreign currency exchange rates					(77)		(1,915)
Cash, cash equivalents, foreign currencies, restricted cash, restricted cash equivalents and restricted foreign currencies, beginning of period					112,443	[1]	359,552	$ 359,552
Cash, cash equivalents, foreign currencies, restricted cash, restricted cash equivalents and restricted foreign currencies, end of period		135,179	[1]	246,384	135,179	[1]	246,384	112,443	[1]
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	[2]				126,960		133,282
Distributions declared for the period		189,189		231,337	189,189		231,337
Supplemental disclosure of non-cash financing activities:
Stock issued in connection with dividend reinvestment plan					0		33,704
Reconciliation of cash and cash equivalents, foreign currencies and restricted cash and cash equivalents and restricted foreign currencies
Cash		19,401			19,401			0
Cash equivalents		46,028			46,028			11,935
Foreign currencies (cost of $6,884 and $11,685, respectively)		6,763			6,763			11,681
Restricted cash		22,777			22,777			7,107
Restricted cash equivalents		40,210			40,210			81,720
Total cash and cash equivalents, foreign currencies, restricted cash and cash equivalents and restricted foreign currencies shown in the Consolidated Statements of Cash Flows		135,179	[1]	246,384	135,179	[1]	246,384	$ 112,443	[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 interest rate swap and forward currency contracts					171		4,697
Forward currency contracts
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		10,258		(5,997)	10,258		(7,203)
Net change in unrealized (appreciation) depreciation on interest rate swap and forward currency contracts		$ (14,042)		$ 15,495	$ (14,334)		$ (6,432)

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