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Shareholders' equity - Accumulated other comprehensive income (Details) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract] |  |
Beginning Balance | $ 2,097,386 | $ 2,066,753
Current period other comprehensive income (loss) | (12,773) | 985
Ending Balance | 2,091,777 | 2,065,588
AOCI |  |
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract] |  |
Beginning Balance | (41,941) | (33,129)
Current period other comprehensive income (loss) | (12,773) | 985
Ending Balance | (54,714) | (32,144)
Net unrealized gains (losses) on securities |  |
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract] |  |
Beginning Balance | (14,951) | (7,931)
Current period other comprehensive income (loss) | (13,297) | 223
Ending Balance | (28,248) | (7,708)
Unrealized gains (losses) on derivatives |  |
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract] |  |
Beginning Balance | 0 | (454)
Current period other comprehensive income (loss) | 0 | 454
Ending Balance | 0 | 0
Retirement benefit plans |  |
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract] |  |
Beginning Balance | (26,990) | (24,744)
Current period other comprehensive income (loss) | 524 | 308
Ending Balance | (26,466) | (24,436)
Hawaiian Electric Company, Inc. and Subsidiaries |  |
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract] |  |
Beginning Balance | 1,845,283 | 1,799,787
Current period other comprehensive income (loss) | 31 | 459
Ending Balance | 1,846,955 | 1,799,769
Hawaiian Electric Company, Inc. and Subsidiaries | AOCI |  |
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract] |  |
Beginning Balance | (1,219) | (322)
Current period other comprehensive income (loss) | 31 | 459
Ending Balance | (1,188) | 137
Hawaiian Electric Company, Inc. and Subsidiaries | Unrealized gains (losses) on derivatives |  |
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract] |  |
Beginning Balance | 0 | (454)
Current period other comprehensive income (loss) | 0 | 454
Ending Balance | 0 | 0
Hawaiian Electric Company, Inc. and Subsidiaries | Retirement benefit plans |  |
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract] |  |
Beginning Balance | (1,219) | 132
Current period other comprehensive income (loss) | 31 | 5
Ending Balance | $ (1,188) | $ 137

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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition Amount after tax of other comprehensive income (loss) attributable to parent entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=64809438&loc=SL4573702-111684 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 19 -URI http://asc.fasb.org/extlink&oid=68079674&loc=SL4569616-111683 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=68079674&loc=SL4569643-111683 + Details
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- Definition Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(30)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 4.E) -URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74512-122707 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(31)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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