Consolidated Statements of Financial Condition (Unaudited) (Parenthetical) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Jun. 30, 2024	Sep. 30, 2023
Statement of Financial Position [Abstract]
Amortized cost	$ 7,965,888	$ 5,593,836
Foreign currencies, cost	6,381	4,540
Restricted foreign currencies, cost	$ 717	$ 0
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	1,000,000	1,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	350,000,000	350,000,000
Common stock, shares issued (in shares)	264,609,056	169,594,742
Common stock, shares outstanding (in shares)	264,609,056	169,594,742