Derivative Instruments and Hedging Activities - Narrative (Details) $ in Thousands	Dec. 31, 2024 USD ($)	Sep. 30, 2024 USD ($)	Dec. 31, 2023 USD ($) security	Sep. 30, 2023 USD ($) security
Bank Term Funding Program Advance
Derivative [Line Items]
Weighted average interest rate (in percent)		4.76%
Certificates of Deposit
Derivative [Line Items]
Weighted average interest rate (in percent)	4.70%
Fair Value Swap | Designated as Hedging Instrument
Derivative [Line Items]
Notional amount	$ 300,000		$ 300,000
Fair Value Swap | Fair Value Hedging | Designated as Hedging Instrument
Derivative [Line Items]
Number of instruments held | security				2
Fair Value Swap, 1 | Fair Value Hedging | Designated as Hedging Instrument
Derivative [Line Items]
Notional amount				$ 250,000
Fair Value Swap, 2 | Fair Value Hedging | Designated as Hedging Instrument
Derivative [Line Items]
Notional amount				$ 50,000
Interest Rate Swap
Derivative [Line Items]
Amount of hedged item	$ 20,000
Interest Rate Swap | Designated as Hedging Instrument
Derivative [Line Items]
Number of instruments held | security			2
Notional amount		$ 125,000
Fixed interest rate (in percent)		3.29%
Interest Rate Swap 1 | Designated as Hedging Instrument
Derivative [Line Items]
Notional amount			$ 100,000
Interest Rate Swap 2 | Designated as Hedging Instrument
Derivative [Line Items]
Notional amount			$ 75,000