Summary of significant accounting policies - Accounts Receivable and Additional Information (Details) - USD ($) $ in Thousands		12 Months Ended
	Aug. 11, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts Receivable
Allowance for customer accounts receivable, accrued unbilled revenues and other accounts receivable		$ 1,500	$ 1,200
Electric utility revenues
Weighted average AFUDC rate	1.75%
Goodwill and other intangibles
Goodwill		82,190	82,190
American Savings Bank (ASB)
Goodwill and other intangibles
Goodwill		82,190	82,190
Low-income housing investments		67,626	59,016
Commitments to fund affordable housing investments		$ 18,100	$ 15,800
American Savings Bank (ASB) | Measurement Band A
Goodwill and other intangibles
Risks inherent in servicing assets and servicing liabilities band percent for risk categorization		0.50%
American Savings Bank (ASB) | Measurement Band B
Goodwill and other intangibles
Risks inherent in servicing assets and servicing liabilities band percent for risk categorization		1.00%
American Savings Bank (ASB) | Loans receivable
Nonperforming loans
Period for classification as delinquent		90 days
American Savings Bank (ASB) | Mortgage receivable
Nonperforming loans
Period for classification as delinquent		180 days
American Savings Bank (ASB) | Consumer
Nonperforming loans
Period for write-off		120 days
Hawaiian Electric Company, Inc. and Subsidiaries
Electric utility revenues
Weighted average AFUDC rate		7.30%	7.70%	7.60%
Hawaiian Electric Company, Inc. and Subsidiaries | Minimum
Contributions in aid of construction
Contributions amortized period		30 years
Hawaiian Electric Company, Inc. and Subsidiaries | Maximum
Contributions in aid of construction
Contributions amortized period		55 years
American Savings Bank (ASB)
Loans modified in a troubled debt restructuring
Number of consecutive months of repayment required for loans to be removed from nonaccrual status		6 months
Goodwill and other intangibles
Goodwill		$ 82,200	$ 82,200