Financial Highlights (Details) $ / shares in Units, $ in Thousands											3 Months Ended		9 Months Ended
	Jun. 13, 2024 $ / shares	May 16, 2024 $ / shares	May 02, 2024 $ / shares	Mar. 01, 2024 $ / shares	Feb. 15, 2024 $ / shares	Dec. 08, 2023 $ / shares	Dec. 01, 2023 $ / shares	Jun. 02, 2023 $ / shares	Mar. 03, 2023 $ / shares	Dec. 09, 2022 $ / shares	Jun. 30, 2024 USD ($) $ / shares shares	Jun. 30, 2023 USD ($) $ / shares shares	Jun. 30, 2024 USD ($) $ / shares shares	Jun. 30, 2023 USD ($) $ / shares shares	Mar. 31, 2024 USD ($)	Sep. 30, 2023 USD ($) shares	Mar. 31, 2023 USD ($)	Sep. 30, 2022 USD ($)	Feb. 06, 2019	Feb. 05, 2019
Investment Company, Financial Highlights [Roll Forward]
Net asset value at beginning of period (in dollars per share)													$ 15.02	$ 14.89
Net increase (decrease) in net assets as a result of issuance of shares (in dollars per share)													0.51	0
Net increase in net assets as a result of repurchases of shares (in dollars per share)													0	0.01
Distributions declared:
From net investment income - after tax (in dollars per share)	$ (0.05)	$ (0.06)	$ (0.39)	$ (0.39)	$ (0.07)	$ (0.37)	$ (0.07)	$ (0.33)	$ (0.33)	$ (0.33)
Net investment income - after tax (in dollars per share)													1.46	1.21
Net realized gain (loss) on investment transactions (in dollars per share)													(0.28)	(0.26)
Net change in unrealized appreciation (depreciation) on investment transactions (in dollars per share)													0.01	(0.03)
Net asset value at end of period (in dollars per share)											$ 15.32	$ 14.83	15.32	14.83
Per share market value at end of period (in dollars per share)											$ 15.71	$ 13.50	$ 15.71	$ 13.50
Total return based on market value													17.41%	17.00%
Number of common shares outstanding (in shares) | shares											264,609,056	169,599,992	264,609,056	169,599,992		169,594,742
Ratio of net investment income - after tax to average net assets													12.92%	10.89%
Ratio of total expenses to average net assets													11.92%	11.60%
Ratio of incentive fee waiver to average net assets													(0.72%)	0.00%
Ratio of incentive fees to average net assets													2.07%	2.09%
Ratio of income and excise taxes to average net assets													0.04%	0.10%
Ratio of net expenses (without incentive fees) to average net assets													9.85%	9.51%
Total return based on average net asset value													6.57%	6.22%
Total return based on average net asset value - annualized													8.78%	8.32%
Net assets at end of period | $											$ 4,053,643	$ 2,515,918	$ 4,053,643	$ 2,515,918	$ 2,593,640	$ 2,547,878	$ 2,506,145	$ 2,544,500
Average debt outstanding | $													$ 3,211,972	$ 3,071,718
Average debt outstanding per share (in dollars per share)													$ 12.14	$ 18.11
Portfolio Turnover													13.11%	13.39%
Asset coverage ratio											192.15%	178.74%	192.15%	178.74%
Asset coverage ratio per unit (in dollars per unit)											$ 1,922	$ 1,787,000	$ 1,922	$ 1,787,000
Minimum asset coverage ratio required																			1.50	1.50
2024 Notes
Distributions declared:
Average debt outstanding | $											$ 38,462	$ 500,000	$ 346,715	$ 500,000
Average market value per unit (in dollars per share)												$ 965,000		$ 965,000
2026 Notes
Distributions declared:
Average debt outstanding | $											$ 600,000	$ 600,000	$ 600,000	$ 600,000
Average market value per unit (in dollars per share)											$ 909,000	$ 863,000	$ 909,000	$ 863,000
2027 Notes
Distributions declared:
Average debt outstanding | $											$ 350,000	$ 350,000	$ 350,000	$ 350,000
Average market value per unit (in dollars per share)											$ 882,000	$ 830,000	$ 882,000	$ 830,000
2028 Notes
Distributions declared:
Average debt outstanding | $											$ 450,000		$ 343,248
Average market value per unit (in dollars per share)											$ 1,027,000		$ 1,027,000
2029 Notes
Distributions declared:
Average debt outstanding | $											$ 600,000		$ 330,657
Average market value per unit (in dollars per share)											$ 980,000		$ 980,000
From net investment income - after tax
Distributions declared:
From net investment income - after tax (in dollars per share)													$ (1.40)	$ (0.99)