Summary of Significant Accounting Policies - Narrative (Details) $ / shares in Units, $ in Thousands		12 Months Ended
	Feb. 08, 2021 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) payment segment branch	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Oct. 27, 2020 USD ($)	Oct. 09, 2013 USD ($)
Summary of Significant Accounting Policies [Line Items]
Number of offices | branch		198
Dividend rate	4.875%
Proceeds from issuance of preferred stock, net	$ 293,325	$ 0	$ 0	$ 293,325
Cash collateral		326,750	$ 284,400
Fair value of NAV		37,587
Remaining unfunded commitment		$ 6,039
Days past grace period to initiate contact to cure deficiency		30 days
Minimum days past due to begin foreclosure proceedings		90 days
Approximate rate reduction concession, minimum		1.00%
Approximate rate reduction concession, maximum		2.00%
Minimum days past due to stop accrual of interest		90 days
Loans returned to full accrual status		90 days
Number of payments required | payment		6
Weighted average remaining contractual term, exercisable		7 years
Number of reportable business segments | segment		1
Civil money penalty from consent order issued					$ 200	$ 34
Minimum
Summary of Significant Accounting Policies [Line Items]
Term for payment and rate reduction		6 months
Award vesting period (in years)		3 years
Minimum | Stock Options and Restricted Stock
Summary of Significant Accounting Policies [Line Items]
Award vesting period (in years)		2 years
Maximum
Summary of Significant Accounting Policies [Line Items]
Term for payment and rate reduction		12 months
Award vesting period (in years)		5 years
Weighted average remaining contractual term, exercisable		10 years
Maximum | Stock Options and Restricted Stock
Summary of Significant Accounting Policies [Line Items]
Award vesting period (in years)		5 years
Public Offering
Summary of Significant Accounting Policies [Line Items]
Number of shares issued in transaction (in shares) | shares	12,000,000
Percentage of preferred stock	2.50%
Public offering price (in usd per share) | $ / shares	$ 25.00
Series A Preferred Stock | Public Offering
Summary of Significant Accounting Policies [Line Items]
Number of shares issued in transaction (in shares) | shares	300,000