Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Sep. 30, 2022
Cash flows from operating activities
Net increase (decrease) in net assets resulting from operations	$ 72,983	$ 15,406	$ 157,067	$ 145,357
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	1,937	1,798	5,362	5,241
Accretion of discounts and amortization of premiums on investments			454	(3,534)
Accretion of discounts and amortization of premiums on issued debt securities			(9,994)	1,294
Net realized (gain) loss on investments			46,555	(15,772)
Net realized (gain) loss on forward currency contracts	(2,021)	(1,080)	(3,192)	(1,080)
Net realized (gain) loss on foreign currency transactions	(1,141)	165	28	(579)
Net change in unrealized (appreciation) depreciation on investments			5,089	8,279
Net change in unrealized (appreciation) depreciation on translation of assets and liabilities in foreign currencies	(3,399)	13,482	(21,857)	18,942
Net change in unrealized (appreciation) depreciation on forward currency contracts	5,431	(11,922)	22,326	(14,059)
Proceeds from (fundings of) revolving loans, net			(2,449)	(2,865)
Fundings of investments			(583,847)	(1,678,450)
Proceeds from principal payments and sales of portfolio investments			550,843	955,184
Proceeds from settlements of forward currency contracts			3,192	1,080
Payment-in-kind interest capitalized	(10,405)	(6,095)	(27,660)	(14,692)
Non-cash dividends	(3,723)	0	(10,767)	0
Changes in operating assets and liabilities:
Interest receivable			(9,139)	(2,308)
Cash collateral held at broker for forward currency contracts			0	6,960
Receivable from investments sold			0	97
Other assets			340	(469)
Interest payable			5,791	7,739
Management and incentive fees payable			4,424	7,496
Payable for investments purchased			250	781
Accrued trustee fees			(72)	173
Accounts payable and other liabilities			(1,497)	(210)
Net cash provided by (used in) operating activities			131,247	(575,395)
Cash flows from financing activities
Borrowings on debt			513,927	1,194,187
Repayments of debt			(463,765)	(594,911)
Capitalized debt issuance costs			(5,368)	(6,379)
Purchases of common stock			(16,791)	0
Distributions paid			(135,311)	(114,985)
Purchases of common stock for dividend reinvestment plan			(33,547)	(25,378)
Net cash provided by (used in) financing activities			(140,855)	452,534
Net change in cash and cash equivalents, foreign currencies, restricted cash and cash equivalents			(9,608)	(122,861)
Effect of foreign currency exchange rates			93	(302)
Cash and cash equivalents, foreign currencies, restricted cash and cash equivalents, beginning of period			180,553	244,343	$ 244,343
Cash and cash equivalents, foreign currencies, restricted cash and cash equivalents, end of period	171,038	121,180	171,038	121,180	180,553
Supplemental disclosure of cash flow information:
Cash paid during the period for interest			98,381	46,115
Distributions declared for the period	168,858	153,537	168,858	153,537
Supplemental disclosure of non-cash financing activities:
Stock issued in connection with dividend reinvestment plan			0	13,174
Reconciliation of cash and cash equivalents, foreign currencies and restricted cash and cash equivalents and restricted foreign currencies
Cash and cash equivalents	85,096		85,096		117,290
Foreign currencies (cost of $6,679 and $7,021, respectively)	6,628		6,628		6,847
Restricted cash and cash equivalents	79,314		79,314		56,416
Total cash and cash equivalents, foreign currencies and restricted cash and cash equivalents shown in the Consolidated Statements of Cash Flows	$ 171,038	$ 121,180	171,038	$ 121,180	180,553
Foreign currencies, cost			$ 6,679		$ 7,021