Financial Highlights - Schedule of Investment Company, Financial Highlights (Details) - USD ($) $ / shares in Units, $ in Thousands					3 Months Ended		6 Months Ended
	Mar. 03, 2023	Dec. 09, 2022	Mar. 04, 2022	Dec. 10, 2021	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Investment Company, Financial Highlights [Roll Forward]
Net asset value at beginning of period (in dollars per share)							$ 14.89	$ 15.19
Net increase in net assets as a result of repurchases of shares (in dollars per share)							0.01	0
Distribution declared (in dollars per share)	$ (0.33)	$ (0.33)	$ (0.30)	$ (0.30)
Net investment income (in dollars per share)							0.77	0.52
Net realized gain (loss) on investment transactions (in dollars per share)							(0.01)	0.08
Net change in unrealized appreciation (depreciation) on investment transactions (in dollars per share)							(0.27)	0.16
Net asset value at end of period (in dollars per share)					$ 14.73	$ 15.35	14.73	15.35
Per share market value at end of period (in dollars per share)					$ 13.56	$ 15.21	$ 13.56	$ 15.21
Total return based on market value							14.90%	0.00%
Number of common shares outstanding (in shares)					170,144,126	170,895,670	170,144,126	170,895,670		170,895,670
Ratio of net investment income to average net assets							10.45%	6.80%
Ratio of total expenses to average net assets							10.60%	6.35%
Ratio of management fee waiver to average net assets(7)							0.00%	(0.07%)
Ratio of incentive fees to average net assets							1.34%	0.30%
Ratio of excise tax to average net assets							0.10%	0.00%
Ratio of net expenses (without incentive fees) to average net assets							9.26%	5.98%
Total return based on average net asset value							3.32%	4.99%
Total return based on average net asset value - annualized							6.67%	10.02%
Net assets at end of period					$ 2,506,145	$ 2,623,549	$ 2,506,145	$ 2,623,549	$ 2,513,685	$ 2,544,500	$ 2,607,479	$ 2,582,692
Average debt outstanding							$ 3,069,131	$ 2,740,594
Average debt outstanding per share (in dollars per share)							$ 18,040.00	$ 16,040.00
Portfolio turnover							14.38%	30.53%
Asset coverage ratio					179.80%	187.55%	179.80%	187.55%
Asset coverage ratio per unit (in dollars per unit)					$ 1,798,000	$ 1,876,000	$ 1,798,000	$ 1,876,000
2024 Notes
Investment Company, Financial Highlights [Roll Forward]
Average debt outstanding					$ 500,000	$ 500,000	$ 500,000	$ 492,308
Average market value per unit (in dollars per share)					$ 963,000	$ 1,017,000	$ 963,000	$ 1,017,000
2026 Notes
Investment Company, Financial Highlights [Roll Forward]
Average debt outstanding					$ 600,000	$ 600,000	$ 600,000	$ 586,813
Average market value per unit (in dollars per share)					$ 862,000	$ 965,000	$ 862,000	$ 965,000
2027 Notes
Investment Company, Financial Highlights [Roll Forward]
Average debt outstanding					$ 350,000	$ 350,000	$ 350,000	$ 350,000
Average market value per unit (in dollars per share)					$ 829,000	$ 943,000	$ 829,000	$ 943,000
From net investment income
Investment Company, Financial Highlights [Roll Forward]
Distribution declared (in dollars per share)							(0.66)	(0.60)
Dividend Reinvestment Plan (DRIP)
Investment Company, Financial Highlights [Roll Forward]
Net increase in net assets as a result of issuance of DRIP shares (in dollars per share)							$ 0	$ 0