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Summary of significant accounting policies - Summary of Income Tax Expense Related to Investment (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Amounts in income taxes related to low-income housing tax credit investments |  |  |
Net benefit to income tax expense | $ (62,807) | $ (40,910) | $ (51,637)
American Savings Bank (ASB) |  |  |
Amounts in income taxes related to low-income housing tax credit investments |  |  |
Net benefit to income tax expense | (29,325) | (11,688) | (23,061)
American Savings Bank (ASB) | Variable Interest Entity, Not Primary Beneficiary |  |  |
Amounts in income taxes related to low-income housing tax credit investments |  |  |
Amortization recognized in the provision for income taxes | (10,300) | (9,600) | (7,900)
Tax credits and other tax benefits recognized in the provision for income taxes | 13,900 | 13,700 | 11,900
Net benefit to income tax expense | $ 3,600 | $ 4,100 | $ 4,000

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