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Fair value measurements - Narrative (Details) | 9 Months Ended
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Sep. 30, 2024 USD ($) | Sep. 30, 2023 USD ($)
Fair value measurements on a nonrecurring basis | American Savings Bank (ASB) |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Adjustments to fair value of loans held for sale | $ 0 | $ 0
Weighted average discount rate |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Mortgage revenue bonds, measurement input | 0.0549 |

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