Summary of Significant Accounting Policies (Details) $ / shares in Units, $ in Thousands		6 Months Ended
	Feb. 08, 2021 USD ($) $ / shares shares	Mar. 31, 2023 USD ($) classOfPortfolioSegment portfolioSegment branch	Sep. 30, 2022 USD ($)
Accounting Policies [Line Items]
Number of bank branches | branch		199
Dividend rate	4.875%
Cash collateral		$ (246,500)	$ (284,400)
Equity method investments		34,260
Unfunded commitment		$ 9,589
Number of portfolio segments | portfolioSegment		2
Loans in process		$ 2,648,512	3,006,023
Commercial loans
Accounting Policies [Line Items]
Number of segment classes | classOfPortfolioSegment		5
Financing Receivable
Accounting Policies [Line Items]
Loans in process		$ 4,533,687	$ 4,947,570
Public Offering
Accounting Policies [Line Items]
Number of depositary shares (in shares) | shares	12,000,000
Proceeds from issuance of preferred stock, net	$ 293,325
Percentage of preferred stock	2.50%
Public offering price (in usd per share) | $ / shares	$ 25.00
Series A Preferred Stock | Public Offering
Accounting Policies [Line Items]
Number of depositary shares (in shares) | shares	300,000