Income taxes - Deferred Tax Assets and Liabilities Due to Book/Tax Differences (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets
Net operating loss	$ 0	$ 0
Allowance for bad debts	24,500	21,781
Other	47,201	43,089
Total deferred tax assets	71,701	64,870
Deferred tax liabilities
Property, plant and equipment	538,484	492,441
Repairs deduction	103,782	104,081
Regulatory assets, excluding amounts attributable to property, plant and equipment	35,107	34,261
Deferred RAM and RBA revenues	26,053	26,400
Retirement benefits	48,400	42,006
Other	48,681	46,558
Total deferred tax liabilities	800,507	745,747
Net deferred income tax liability	728,806	680,877
Hawaiian Electric Company, Inc. and Subsidiaries
Deferred tax assets
Net operating loss	9,158	37,283
Allowance for bad debts	2,364	1,852
Other	18,720	18,386
Total deferred tax assets	30,242	57,521
Deferred tax liabilities
Property, plant and equipment	536,885	489,884
Repairs deduction	103,782	104,081
Regulatory assets, excluding amounts attributable to property, plant and equipment	35,107	34,261
Deferred RAM and RBA revenues	26,053	26,400
Retirement benefits	51,445	44,991
Other	10,629	12,710
Total deferred tax liabilities	763,901	712,327
Net deferred income tax liability	$ 733,659	$ 654,806