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Summary of significant accounting policies - Leases and Additional Information (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Leases |  |  |
Operating lease expense | $ 20,000 | $ 19,000 | $ 18,000
Future minimum lease payments |  |  |
2018 | 11,000 |  |
2019 | 10,000 |  |
2020 | 8,000 |  |
2021 | 7,000 |  |
2022 | 4,000 |  |
Thereafter | 36,000 |  |
Total | 76,000 |  |
Reclass of AOCI for tax rate reduction impact | 0 |  |
Retained earnings |  |  |
Future minimum lease payments |  |  |
Reclass of AOCI for tax rate reduction impact | 7,440 |  |
Retained earnings | Accounting Standards Update 2018-02 |  |  |
Future minimum lease payments |  |  |
Reclass of AOCI for tax rate reduction impact | 7,400 |  |
AOCI |  |  |
Future minimum lease payments |  |  |
Reclass of AOCI for tax rate reduction impact | (7,440) |  |
AOCI | Accounting Standards Update 2018-02 |  |  |
Future minimum lease payments |  |  |
Reclass of AOCI for tax rate reduction impact | (7,400) |  |
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Leases |  |  |
Operating lease expense | 11,000 | $ 10,000 | $ 9,000
Future minimum lease payments |  |  |
2018 | 6,000 |  |
2019 | 5,000 |  |
2020 | 5,000 |  |
2021 | 5,000 |  |
2022 | 3,000 |  |
Thereafter | 29,000 |  |
Total | 53,000 |  |
Reclass of AOCI for tax rate reduction impact | 0 |  |
Hawaiian Electric Company, Inc. and Subsidiaries | Retained earnings |  |  |
Future minimum lease payments |  |  |
Reclass of AOCI for tax rate reduction impact | 209 |  |
Hawaiian Electric Company, Inc. and Subsidiaries | Retained earnings | Accounting Standards Update 2018-02 |  |  |
Future minimum lease payments |  |  |
Reclass of AOCI for tax rate reduction impact | 200 |  |
Hawaiian Electric Company, Inc. and Subsidiaries | AOCI |  |  |
Future minimum lease payments |  |  |
Reclass of AOCI for tax rate reduction impact | (209) |  |
Hawaiian Electric Company, Inc. and Subsidiaries | AOCI | Accounting Standards Update 2018-02 |  |  |
Future minimum lease payments |  |  |
Reclass of AOCI for tax rate reduction impact | $ (200) |  |

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- Definition Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 10 -Section 55 -Paragraph 40 -Subparagraph (Note 3) -URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717 + Details
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