Income taxes - Deferred Tax Assets and Liabilities Due to Book/Tax Differences (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets
Regulatory liabilities, excluding amounts attributable to property, plant and equipment	$ 93,684	$ 100,427
Operating lease liabilities	41,582	51,573
Revenue taxes	22,726	20,922
Allowance for bad debts	31,973	14,858
Other	44,127	33,106
Total deferred tax assets	234,092	220,886
Deferred tax liabilities
Property, plant and equipment related	487,209	464,312
Operating lease right-of-use assets	41,370	51,542
Regulatory assets, excluding amounts attributable to property, plant and equipment	25,841	33,897
Retirement benefits	18,407	9,684
Other	56,354	40,776
Total deferred tax liabilities	629,181	600,211
Net deferred income tax liability	395,089	379,325
Deferred tax assets, tax credit carryforwards	10,900
Hawaiian Electric Company, Inc. and Subsidiaries
Deferred tax assets
Regulatory liabilities, excluding amounts attributable to property, plant and equipment	93,684	100,427
Operating lease liabilities	34,586	45,608
Revenue taxes	22,726	20,922
Allowance for bad debts	4,835	560
Other	24,741	20,259
Total deferred tax assets	180,572	187,776
Deferred tax liabilities
Property, plant and equipment related	473,734	458,349
Operating lease right-of-use assets	34,586	45,608
Regulatory assets, excluding amounts attributable to property, plant and equipment	25,841	33,897
Retirement benefits	20,537	13,072
Other	23,672	14,001
Total deferred tax liabilities	578,370	564,927
Net deferred income tax liability	397,798	$ 377,151
Deferred tax assets, tax credit carryforwards	5,800
State and Local Jurisdiction
Deferred tax liabilities
Tax credit carryforward	14,600
State and Local Jurisdiction | Hawaiian Electric Company, Inc. and Subsidiaries
Deferred tax liabilities
Tax credit carryforward	$ 7,800