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Credit agreements and long-term debt (Details) | 1 Months Ended |  |
--- | --- | --- | ---
Jun. 30, 2018 USD ($) Institution | May 30, 2018 USD ($) | Dec. 31, 2017 USD ($)
Debt Disclosure [Abstract] |  |  |
Number of financial institutions | Institution | 8 |  |
Line of credit facility |  |  |
Credit agreement |  |  |
Revolving noncollateralized credit facility with a letter of credit sub-facility | $ 150,000,000 |  |
Amount outstanding under facilities | 0 |  | $ 0
Line of credit facility | Hawaiian Electric Company |  |  |
Credit agreement |  |  |
Revolving noncollateralized credit facility with a letter of credit sub-facility | 200,000,000 |  |
Amount outstanding under facilities | 0 |  | $ 0
Unsecured Debt | Mauo, LLC |  |  |
Credit agreement |  |  |
Aggregate principal amount | 0 |  |
Debt, face amount | $ 50,500,000 |  |
Unsecured Debt | Mauo, LLC | London Interbank Offered Rate (LIBOR) |  |  |
Credit agreement |  |  |
Basis spread on variable rate | 1.375% |  |
Unsecured Debt | Series 2018A |  |  |
Credit agreement |  |  |
Aggregate principal amount |  | $ 67,500,000 |
Fixed coupon interest rate |  | 4.38% |
Unsecured Debt | Series 2018A | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Credit agreement |  |  |
Aggregate principal amount |  | $ 52,000,000 |
Unsecured Debt | Series 2018A | Hawaii Electric Light Company, Inc. (HELCO) |  |  |
Credit agreement |  |  |
Aggregate principal amount |  | 9,000,000 |
Unsecured Debt | Series 2018A | Maui Electric |  |  |
Credit agreement |  |  |
Aggregate principal amount |  | 6,500,000 |
Unsecured Debt | Series 2018B |  |  |
Credit agreement |  |  |
Aggregate principal amount |  | $ 17,500,000 |
Fixed coupon interest rate |  | 4.53% |
Unsecured Debt | Series 2018B | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Credit agreement |  |  |
Aggregate principal amount |  | $ 12,500,000 |
Unsecured Debt | Series 2018B | Hawaii Electric Light Company, Inc. (HELCO) |  |  |
Credit agreement |  |  |
Aggregate principal amount |  | 3,000,000 |
Unsecured Debt | Series 2018B | Maui Electric |  |  |
Credit agreement |  |  |
Aggregate principal amount |  | 2,000,000 |
Unsecured Debt | Series 2018C |  |  |
Credit agreement |  |  |
Aggregate principal amount |  | $ 15,000,000 |
Fixed coupon interest rate |  | 4.72% |
Unsecured Debt | Series 2018C | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Credit agreement |  |  |
Aggregate principal amount |  | $ 10,500,000 |
Unsecured Debt | Series 2018C | Hawaii Electric Light Company, Inc. (HELCO) |  |  |
Credit agreement |  |  |
Aggregate principal amount |  | 3,000,000 |
Unsecured Debt | Series 2018C | Maui Electric |  |  |
Credit agreement |  |  |
Aggregate principal amount |  | $ 1,500,000 |

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- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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