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Summary of significant accounting policies - Accounts Receivable and Additional Information (Details) - USD ($) $ in Thousands |  | 12 Months Ended
--- | --- | ---
Aug. 11, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Accounts Receivable |  |  |  |
Allowance for customer accounts receivable, accrued unbilled revenues and other accounts receivable |  | $ 1,200 | $ 1,100 |
Electric utility revenues |  |  |  |
Weighted average AFUDC rate | 1.75% |  |  |
Goodwill and other intangibles |  |  |  |
Goodwill |  | 82,190 | 82,190 |
American Savings Bank (ASB) |  |  |  |
Goodwill and other intangibles |  |  |  |
Goodwill |  | 82,190 | 82,190 |
Affordable housing investment, carrying value |  | 59,016 | 47,081 |
Commitments to fund affordable housing investments |  | $ 15,800 | 14,000 |
American Savings Bank (ASB) | Loans receivable |  |  |  |
Nonperforming loans |  |  |  |
Period for classification as delinquent |  | 90 days |  |
American Savings Bank (ASB) | Mortgage receivable |  |  |  |
Nonperforming loans |  |  |  |
Period for classification as delinquent |  | 180 days |  |
American Savings Bank (ASB) | Consumer |  |  |  |
Nonperforming loans |  |  |  |
Period for write-off |  | 120 days |  |
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |  |
Electric utility revenues |  |  |  |
Revenue taxes included in revenues and in taxes, other than income taxes expense |  | $ 202,000 | 187,000 | $ 209,000
Revenue taxes accrued |  | $ 115,000 | $ 104,000 |
Weighted average AFUDC rate |  | 7.70% | 7.60% | 7.60%
Hawaiian Electric Company, Inc. and Subsidiaries | Minimum |  |  |  |
Contributions in aid of construction |  |  |  |
Contributions amortized period |  | 30 years |  |
Hawaiian Electric Company, Inc. and Subsidiaries | Maximum |  |  |  |
Contributions in aid of construction |  |  |  |
Contributions amortized period |  | 55 years |  |
American Savings Bank (ASB) |  |  |  |
Loans modified in a troubled debt restructuring |  |  |  |
Number of consecutive months of repayment required for loans to be removed from nonaccrual status |  | 6 months |  |
Goodwill and other intangibles |  |  |  |
Goodwill |  | $ 82,200 | $ 82,200 |

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