Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022	Sep. 30, 2022
Cash flows from operating activities
Net increase (decrease) in net assets resulting from operations	$ 58,503	$ 66,873	$ 84,084	$ 129,951
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	1,677	1,776	3,425	3,443
Accretion of discounts and amortization of premiums on investments			(6,904)	(1,748)
Accretion of discounts and amortization of premiums on issued debt securities			484	879
Net realized (gain) loss on investments			1,470	(14,176)
Net realized (gain) loss on forward currency contracts	(708)	0	(1,171)	0
Net realized (gain) loss on foreign currency transactions	(17)	(227)	1,169	(744)
Net change in unrealized (appreciation) depreciation on investments			48,171	(30,716)
Net change in unrealized (appreciation) depreciation on translation of assets and liabilities in foreign currencies	(2,561)	4,663	(18,458)	5,460
Net change in unrealized (appreciation) depreciation on forward currency contracts	2,447		16,895	(2,137)
Proceeds from (fundings of) revolving loans, net			(1,970)	(1,002)
Fundings of investments			(412,649)	(1,267,348)
Proceeds from principal payments and sales of portfolio investments			393,997	783,967
Proceeds from settlements of forward currency contracts			1,171	0
Payment-in-kind interest capitalized	(9,478)	(5,124)	(17,255)	(8,597)
Non-cash dividends	(3,595)	0	(7,044)	0
Changes in operating assets and liabilities:
Interest receivable			(10,446)	(2,990)
Cash collateral held at broker for forward currency contracts			0	6,960
Receivable from investments sold			0	97
Other assets			164	(717)
Interest payable			3,190	3,127
Management and incentive fees payable			3,223	8,682
Payable for investments purchased			0	(294)
Accrued trustee fees			(187)	0
Accounts payable and other liabilities			1,344	(1,121)
Net cash provided by (used in) operating activities			82,703	(389,024)
Cash flows from financing activities
Borrowings on debt			312,251	916,760
Repayments of debt			(310,100)	(502,300)
Capitalized debt issuance costs			(5,368)	(6,379)
Purchases of common stock			(9,647)	0
Distributions paid			(90,793)	(75,649)
Purchases of common stock for dividend reinvestment plan			(21,999)	(13,445)
Net cash provided by (used in) financing activities			(125,656)	318,987
Net change in cash and cash equivalents, foreign currencies, restricted cash and cash equivalents			(42,953)	(70,037)
Effect of foreign currency exchange rates			96	26
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	137,696	174,332	137,696	174,332	180,553
Supplemental disclosure of cash flow information:
Cash paid during the period for interest			63,401	29,663
Distributions declared during the period	112,792	102,268	112,792	102,268
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	76,757		76,757		117,290
Foreign currencies (cost of $10,547 and $7,021, respectively)	10,716		10,716		6,847
Restricted cash and cash equivalents	50,223		50,223		56,416
Total cash and cash equivalents, foreign currencies and restricted cash and cash equivalents shown in the Consolidated Statements of Cash Flows	$ 137,696	$ 174,332	137,696	$ 174,332	180,553
Foreign currencies, cost			$ 10,547		$ 7,021