Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023
Statement of Financial Position [Abstract]
Interest-earning deposits	$ 287,748	$ 213,830
Available-for-sale securities, amortized cost	721,612	1,385,992
Loans receivable, allowance for credit losses	$ 24,178	$ 23,759
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	1,400,000,000	1,400,000,000
Common stock, shares issued	133,908,375	135,936,375
Common stock, shares outstanding	133,908,375	135,936,375