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Shareholders' equity - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
AOCI Attributable to Parent [Roll Forward] |  |  |
Beginning Balance | $ 2,066,753 | $ 1,927,640 | $ 1,790,573
Other comprehensive income (loss), net of taxes | (1,372) | (6,867) | 1,116
Reclass of AOCI for tax rate reduction impact | 0 |  |
Ending Balance | 2,097,386 | 2,066,753 | 1,927,640
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
AOCI Attributable to Parent [Roll Forward] |  |  |
Beginning Balance | 1,799,787 | 1,728,325 | 1,682,144
Other comprehensive income (loss), net of taxes | (688) | (1,247) | 880
Reclass of AOCI for tax rate reduction impact | 0 |  |
Ending Balance | 1,845,283 | 1,799,787 | 1,728,325
AOCI |  |  |
AOCI Attributable to Parent [Roll Forward] |  |  |
Beginning Balance | (33,129) | (26,262) | (27,378)
Other comprehensive income (loss), net of taxes | (1,372) | (6,867) | 1,116
Reclass of AOCI for tax rate reduction impact | (7,440) |  |
Ending Balance | (41,941) | (33,129) | (26,262)
AOCI | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
AOCI Attributable to Parent [Roll Forward] |  |  |
Beginning Balance | (322) | 925 | 45
Other comprehensive income (loss), net of taxes | (688) | (1,247) | 880
Reclass of AOCI for tax rate reduction impact | (209) |  |
Ending Balance | (1,219) | (322) | 925
Net unrealized gains (losses) on securities |  |  |
AOCI Attributable to Parent [Roll Forward] |  |  |
Beginning Balance | (7,931) | (1,872) | 462
Other comprehensive income (loss), net of taxes | (4,370) | (6,059) | (2,334)
Reclass of AOCI for tax rate reduction impact | (2,650) |  |
Ending Balance | (14,951) | (7,931) | (1,872)
Unrealized gains (losses) on derivatives |  |  |
AOCI Attributable to Parent [Roll Forward] |  |  |
Beginning Balance | (454) | (54) | (289)
Other comprehensive income (loss), net of taxes | 454 | (400) | 235
Reclass of AOCI for tax rate reduction impact | 0 |  |
Ending Balance | 0 | (454) | (54)
Unrealized gains (losses) on derivatives | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
AOCI Attributable to Parent [Roll Forward] |  |  |
Beginning Balance | (454) | 0 | 0
Other comprehensive income (loss), net of taxes | 454 | (454) | 0
Reclass of AOCI for tax rate reduction impact | 0 |  |
Ending Balance | 0 | (454) | 0
Retirement benefit plans |  |  |
AOCI Attributable to Parent [Roll Forward] |  |  |
Beginning Balance | (24,744) | (24,336) | (27,551)
Other comprehensive income (loss), net of taxes | 2,544 | (408) | 3,215
Reclass of AOCI for tax rate reduction impact | (4,790) |  |
Ending Balance | (26,990) | (24,744) | (24,336)
Retirement benefit plans | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
AOCI Attributable to Parent [Roll Forward] |  |  |
Beginning Balance | 132 | 925 | 45
Other comprehensive income (loss), net of taxes | (1,142) | (793) | 880
Reclass of AOCI for tax rate reduction impact | (209) |  |
Ending Balance | $ (1,219) | $ 132 | $ 925

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- Definition Tax Cuts And Jobs Act Of 2017, Reclassification From AOCI To Retained Earnings + References No definition available. + Details
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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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