Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Statement of Financial Position [Abstract]
Interest-earning deposits	$ 24,289	$ 172,430
Available-for-sale securities, Amortized Cost	2,008,456
Available-for-sale securities, Amortized cost		1,529,605
Loans receivable, allowance for credit losses	$ 19,823
Loans receivable, allowance for credit losses		$ 31,527
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	138,832,284	138,956,296
Common stock, shares outstanding	138,832,284	138,956,296