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Long-term debt (Details) - USD ($) |  |  |  | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Nov. 20, 2017 | Oct. 06, 2017 | Jun. 29, 2017 | Dec. 31, 2017 | Dec. 26, 2017 | Dec. 14, 2017 | Dec. 31, 2016
Long-term debt |  |  |  |  |  |  |
Long-term debt, net—other than bank |  |  |  | $ 1,683,797,000 |  |  | $ 1,619,019,000
Less unamortized debt issuance costs |  |  |  | (2,007,000) |  |  | (241,000)
Aggregate principal payments |  |  |  |  |  |  |
2018 |  |  |  | 54,000,000 |  |  |
2019 |  |  |  | 4,000,000 |  |  |
2020 |  |  |  | 100,000,000 |  |  |
2021 |  |  |  | 54,000,000 |  |  |
2022 |  |  |  | 206,000,000 |  |  |
Electric utility |  |  |  |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
2018 |  |  |  | 50,000,000 |  |  |
2019 |  |  |  | 0 |  |  |
2020 |  |  |  | 96,000,000 |  |  |
2021 |  |  |  | 0 |  |  |
2022 |  |  |  | $ 52,000,000 |  |  |
Senior notes | Hamakua Energy Partners, L.P. (HEP) |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Debt instrument, stated interest rate |  |  |  |  | 4.02% |  |
Aggregate principal payments |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  |  | $ 67,300,000 |  |
Term loan | Hamakua Energy Partners, L.P. (HEP) |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Debt instrument, stated interest rate |  |  |  | 4.02% |  |  |
Special purpose revenue bonds issued on behalf of electric utility subsidiaries |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Long-term debt, net—other than bank |  |  |  | $ 1,368,479,000 |  |  | 1,319,260,000
Hamakua Energy, LLC Loan at 4.02% Due 2030 | Senior notes |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Gross long-term debt |  |  |  | $ 67,325,000 |  |  | 0
Debt instrument, stated interest rate |  |  |  | 4.02% |  |  |
Senior Notes 2.99% Due 2022 | Senior notes |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Gross long-term debt |  |  |  | $ 150,000,000 |  |  | 0
Senior Notes 2.99% Due 2022 | Term loan |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Debt instrument, stated interest rate |  |  |  | 2.99% |  |  |
HEI 5.67% senior notes, due 2021 | Senior notes |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Gross long-term debt |  |  |  | $ 50,000,000 |  |  | 50,000,000
Debt instrument, stated interest rate |  |  |  | 5.67% |  |  |
HEI 3.99% senior notes, due 2023 | Senior notes |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Gross long-term debt |  |  |  | $ 50,000,000 |  |  | 50,000,000
Debt instrument, stated interest rate |  |  |  | 3.99% |  |  |
HEI Term loans (LIBOR 0.75%), paid in 2017 |  |  |  |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
Aggregate repurchased principal amount | $ 75,000,000 |  |  |  |  |  |
HEI Term loans (LIBOR 0.75%), paid in 2017 | Term loan |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Gross long-term debt |  |  |  | $ 0 |  |  | $ 200,000,000
HEI Term loans (LIBOR 0.75%), paid in 2017 | Term loan | LIBOR |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Line of credit facility basis point spread |  |  |  | 0.00% |  |  |
Eurodollar Term Loan | Unsecured Debt |  |  |  |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
Proceeds from issuance of debt |  | $ 125,000,000 |  |  |  |  |
Debt instrument term |  | 364 days |  |  |  |  |
Aggregate repurchased principal amount |  | $ 125,000,000 |  |  |  |  |
Debt instrument, face amount | 125,000,000 |  |  |  |  |  |
Repayments of unsecured debt | $ 75,000,000 |  |  |  |  |  |
Refunding Series 2007B Special Purpose Revenue Bonds |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Debt instrument, stated interest rate |  |  |  | 4.60% |  |  |
Refunding Series 2007B Special Purpose Revenue Bonds | Unsecured Debt |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Debt instrument, stated interest rate |  |  | 4.60% |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
Aggregate repurchased principal amount |  |  | $ 125,000,000 |  |  |  |
Bank of America Loan Agreement |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Debt instrument, stated interest rate | 2.99% |  |  |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
Debt instrument, face amount | $ 150,000,000 |  |  |  |  |  |
Refunding Series 2017A Special Purpose Revenue Bonds | Unsecured Debt |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Debt instrument, stated interest rate |  |  | 3.10% |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
Debt instrument, face amount |  |  | $ 125,000,000 |  |  |  |
Refunding Series 2017A Special Purpose Revenue Bonds | Unsecured Debt | Hawaiian Electric Company, Inc (HECO) |  |  |  |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
Proceeds from issuance of debt |  |  | 62,000,000 |  |  |  |
Refunding Series 2017A Special Purpose Revenue Bonds | Unsecured Debt | HELCO |  |  |  |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
Proceeds from issuance of debt |  |  | 8,000,000 |  |  |  |
Refunding Series 2017A Special Purpose Revenue Bonds | Unsecured Debt | MECO |  |  |  |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
Proceeds from issuance of debt |  |  | $ 55,000,000 |  |  |  |
Refunding Series 2017B Special Purpose Revenue Bonds | Unsecured Debt |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Debt instrument, stated interest rate |  |  | 4.00% |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
Debt instrument, face amount |  |  | $ 140,000,000 |  |  |  |
Refunding Series 2017B Special Purpose Revenue Bonds | Unsecured Debt | Hawaiian Electric Company, Inc (HECO) |  |  |  |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
Proceeds from issuance of debt |  |  | 100,000,000 |  |  |  |
Refunding Series 2017B Special Purpose Revenue Bonds | Unsecured Debt | HELCO |  |  |  |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
Proceeds from issuance of debt |  |  | 20,000,000 |  |  |  |
Refunding Series 2017B Special Purpose Revenue Bonds | Unsecured Debt | MECO |  |  |  |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
Proceeds from issuance of debt |  |  | $ 20,000,000 |  |  |  |
Series 2007A Special Purpose Revenue Bonds | Unsecured Debt |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Debt instrument, stated interest rate |  |  | 4.65% |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
Aggregate repurchased principal amount |  |  | $ 140,000,000 |  |  |  |
4.31%, Series 2017A, due 2047 |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Debt instrument, stated interest rate |  |  |  | 4.31% |  |  |
4.31%, Series 2017A, due 2047 | Electric utility |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |
Debt instrument, stated interest rate |  |  |  |  |  | 4.31% |
Aggregate principal payments |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  |  |  | $ 40,000,000 |
4.31%, Series 2017A, due 2047 | MECO |  |  |  |  |  |  |
Aggregate principal payments |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  |  |  | $ 10,000,000 |

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