Allowance for Losses on Loans - Narrative (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | |||
|---|---|---|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
Mar. 31, 2026 |
Mar. 31, 2025 |
Sep. 30, 2025 |
|
| Accounts, Notes, Loans and Financing Receivable [Line Items] | |||||
| Provision for credit losses | $ 4,000 | $ 2,750 | $ 7,500 | $ 2,750 | |
| Allowance for credit loss, charge-off (recovery) | 589 | $ 5,063 | 4,270 | $ 5,294 | |
| Gross loans | $ 20,168,933 | $ 20,168,933 | $ 20,288,338 | ||
| Non-accrual percent of total loans | 0.61% | 0.61% | 0.63% | ||
| Delinquency percent, past due | 0.78% | 0.78% | 0.60% | ||
| Financial Asset Originated | |||||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | |||||
| Non-accrual loans | $ 123,859 | $ 123,859 | $ 128,628 | ||
| Non-Performing Loans | |||||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | |||||
| Gross loans | $ 131,984 | $ 131,984 | $ 143,022 | ||
| Ratio of non-performing assets to total assets | 0.48% | 0.48% | 0.54% | ||