Consolidated Statements of Financial Condition (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Statement of Financial Position [Abstract]
Amortized Cost	$ 5,569,604	$ 4,895,397
Foreign currencies, cost	7,021	5,145
Restricted foreign currencies, cost	$ 0	$ 1,442
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	200,000,000
Common stock, shares issued (in shares)	170,895,670	170,028,584
Common stock, shares outstanding (in shares)	170,895,670	170,028,584