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Bank segment (HEI only) - Statements of Comprehensive Income - Additional Information (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Condensed Statement of Income Captions [Line Items] |  |  |
Net unrealized loss on available-for-sale securities, tax benefits | $ (2,886) | $ (3,763) | $ (1,541)
Reclassification adjustment for net realized gains included in net income, taxes | 0 | 238 | 0
Net gains (losses) arising during the period, retirement benefits, taxes | 41,129 | (27,703) | 3,753
Amortization of net loss, prior service gain and transition obligation included in net periodic benefit cost, tax benefits | (10,041) | (9,267) | (14,344)
American Savings Bank (ASB) |  |  |
Condensed Statement of Income Captions [Line Items] |  |  |
Net unrealized loss on available-for-sale securities, tax benefits | (2,886) | (3,763) | (1,541)
Reclassification adjustment for net realized gains included in net income, taxes | 0 | 238 | 0
Net gains (losses) arising during the period, retirement benefits, taxes | 0 | 0 | 59
Amortization of net loss, prior service gain and transition obligation included in net periodic benefit cost, tax benefits | $ (812) | $ (566) | $ (1,011)

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- Definition Amount of tax expense (benefit) related to (increase) decrease in the value of the projected benefit obligation related to a change in an actuarial assumption and increase (decrease) in the value of the plan assets resulting from experience different from that assumed, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e640-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i-k) -URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580 + Details
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- Definition Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27357-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e640-108580 + Details
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- Definition Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e640-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (e,f) -URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580 + Details
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