Income taxes - Deferred Tax Assets and Liabilities Due to Book/Tax Differences (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets
Regulatory liabilities, excluding amounts attributable to property, plant and equipment	$ 100,427	$ 104,868
Operating lease liabilities	51,573
Allowance for bad debts	14,858	14,647
Other	54,028	46,036
Total deferred tax assets	220,886	165,551
Deferred tax liabilities
Property, plant and equipment related	464,312	437,644
Operating lease right-of-use assets	51,542
Regulatory assets, excluding amounts attributable to property, plant and equipment	33,897	37,345
Deferred RAM and RBA revenues	0	11,278
Retirement benefits	9,684	20,173
Other	40,776	31,629
Total deferred tax liabilities	600,211	538,069
Net deferred income tax liability	379,325	372,518
Deferred tax assets, tax credit carryforwards	8,700
Hawaiian Electric Company, Inc. and Subsidiaries
Deferred tax assets
Regulatory liabilities, excluding amounts attributable to property, plant and equipment	100,427	104,868
Operating lease liabilities	45,608
Allowance for bad debts	560	659
Other	41,181	26,522
Total deferred tax assets	187,776	132,049
Deferred tax liabilities
Property, plant and equipment related	458,349	434,831
Operating lease right-of-use assets	45,608
Regulatory assets, excluding amounts attributable to property, plant and equipment	33,897	37,345
Deferred RAM and RBA revenues	0	11,278
Retirement benefits	13,072	25,430
Other	14,001	6,362
Total deferred tax liabilities	564,927	515,246
Net deferred income tax liability	377,151	$ 383,197
Deferred tax assets, tax credit carryforwards	6,700
State and Local Jurisdiction
Deferred tax liabilities
Tax credit carryforward	11,700
State and Local Jurisdiction | Hawaiian Electric Company, Inc. and Subsidiaries
Deferred tax liabilities
Tax credit carryforward	$ 9,000