Electric utility segment - Condensed consolidating balance sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Utility property, plant and equipment
Total property, plant and equipment, net	$ 4,867,127	$ 4,830,118
Current assets
Cash and cash equivalents	186,407	169,208	$ 244,785	$ 261,881
Other long-term assets
Operating lease right-of-use assets	241,486	0
Total assets	13,360,105	13,104,051
Capitalization
Total shareholders’ equity	2,183,515	2,162,280	2,091,777	2,097,386
Cumulative preferred stock—not subject to mandatory redemption	0	0
Current liabilities
Interest and preferred dividends payable	33,711	28,254
Deferred credits and other liabilities
Deferred income taxes	375,330	372,518
Total liabilities and shareholders’ equity	13,360,105	13,104,051
Consolidating adjustments
Utility property, plant and equipment
Land	0	0
Plant and equipment	0	0
Less accumulated depreciation	0	0
Construction in progress	0	0
Utility property, plant and equipment, net	0	0
Nonutility property, plant and equipment, less accumulated depreciation	0	0
Total property, plant and equipment, net	0	0
Investment in wholly owned subsidiaries, at equity	(582,374)	(576,838)
Current assets
Cash and cash equivalents	0	0	0	0
Advances to affiliates	(18,700)
Customer accounts receivable, net	0	0
Accrued unbilled revenues, net	0	0
Other accounts receivable, net	(6,828)	(21,911)
Fuel oil stock, at average cost	0	0
Materials and supplies, at average cost	0	0
Prepayments and other	0	0
Regulatory assets	0	0
Total current assets	(25,528)	(21,911)
Other long-term assets
Operating lease right-of-use assets	0
Regulatory assets	0	0
Other	0	0
Total other long-term assets	0	0
Total assets	(607,902)	(598,749)
Capitalization
Total shareholders’ equity	(582,374)	(576,838)	(559,511)	(557,013)
Cumulative preferred stock—not subject to mandatory redemption	0	0
Long-term debt, net	0	0
Total capitalization	(582,374)	(576,838)
Current liabilities
Current portion of operating lease liabilities	0
Current portion of long-term debt	0
Short-term borrowings from non-affiliates	0	0
Short-term borrowings from affiliate	(18,700)
Accounts payable	0	0
Interest and preferred dividends payable	(23)	(32)
Taxes accrued	0	0
Regulatory liabilities	0	0
Other	(6,805)	(21,879)
Total current liabilities	(25,528)	(21,911)
Deferred credits and other liabilities
Operating lease liabilities	0
Deferred income taxes	0	0
Regulatory liabilities	0	0
Unamortized tax credits	0	0
Defined benefit pension and other postretirement benefit plans liability	0	0
Other	0	0
Total deferred credits and other liabilities	0	0
Total liabilities and shareholders’ equity	(607,902)	(598,749)
Hawaiian Electric (parent only) | Reportable Legal Entities
Utility property, plant and equipment
Land	40,449	40,449
Plant and equipment	4,505,063	4,456,090
Less accumulated depreciation	(1,548,895)	(1,523,861)
Construction in progress	200,399	193,677
Utility property, plant and equipment, net	3,197,016	3,166,355
Nonutility property, plant and equipment, less accumulated depreciation	5,313	5,314
Total property, plant and equipment, net	3,202,329	3,171,669
Investment in wholly owned subsidiaries, at equity	582,374	576,838
Current assets
Cash and cash equivalents	2,994	16,732	11,988	2,059
Advances to affiliates	9,500
Customer accounts receivable, net	94,489	125,960
Accrued unbilled revenues, net	69,315	88,060
Other accounts receivable, net	10,667	21,962
Fuel oil stock, at average cost	91,090	54,262
Materials and supplies, at average cost	30,766	30,291
Prepayments and other	25,940	23,214
Regulatory assets	60,374	60,093
Total current assets	395,135	420,574
Other long-term assets
Operating lease right-of-use assets	219,246
Regulatory assets	530,424	537,708
Other	71,528	69,749
Total other long-term assets	821,198	607,457
Total assets	5,001,036	4,776,538
Capitalization
Total shareholders’ equity	1,964,478	1,957,641	1,846,955	1,845,283
Cumulative preferred stock—not subject to mandatory redemption	22,293	22,293
Long-term debt, net	938,284	1,000,137
Total capitalization	2,925,055	2,980,071
Current liabilities
Current portion of operating lease liabilities	61,149
Current portion of long-term debt	61,968
Short-term borrowings from non-affiliates	55,999	25,000
Short-term borrowings from affiliate	9,200
Accounts payable	120,366	126,384
Interest and preferred dividends payable	19,629	16,203
Taxes accrued	135,189	164,747
Regulatory liabilities	3,981	7,699
Other	45,380	46,391
Total current liabilities	512,861	386,424
Deferred credits and other liabilities
Operating lease liabilities	157,980
Deferred income taxes	271,098	271,438
Regulatory liabilities	664,229	657,210
Unamortized tax credits	60,323	60,271
Defined benefit pension and other postretirement benefit plans liability	359,109	359,174
Other	50,381	61,950
Total deferred credits and other liabilities	1,563,120	1,410,043
Total liabilities and shareholders’ equity	5,001,036	4,776,538
HELCO | Reportable Legal Entities
Utility property, plant and equipment
Land	5,606	5,606
Plant and equipment	1,262,332	1,259,553
Less accumulated depreciation	(554,438)	(547,848)
Construction in progress	14,520	8,781
Utility property, plant and equipment, net	728,020	726,092
Nonutility property, plant and equipment, less accumulated depreciation	115	115
Total property, plant and equipment, net	728,135	726,207
Investment in wholly owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	3,825	15,623	5,080	4,025
Advances to affiliates	9,200
Customer accounts receivable, net	23,373	26,483
Accrued unbilled revenues, net	13,398	17,051
Other accounts receivable, net	1,447	3,131
Fuel oil stock, at average cost	10,796	11,027
Materials and supplies, at average cost	8,037	7,155
Prepayments and other	3,944	5,212
Regulatory assets	2,993	3,177
Total current assets	77,013	88,859
Other long-term assets
Operating lease right-of-use assets	1,605
Regulatory assets	118,315	120,658
Other	16,076	15,944
Total other long-term assets	135,996	136,602
Total assets	941,144	951,668
Capitalization
Total shareholders’ equity	298,497	295,874	288,927	286,647
Cumulative preferred stock—not subject to mandatory redemption	7,000	7,000
Long-term debt, net	217,775	217,749
Total capitalization	523,272	520,623
Current liabilities
Current portion of operating lease liabilities	91
Current portion of long-term debt	0
Short-term borrowings from non-affiliates	0	0
Short-term borrowings from affiliate	0
Accounts payable	14,391	20,045
Interest and preferred dividends payable	4,073	4,203
Taxes accrued	29,238	34,128
Regulatory liabilities	3,882	4,872
Other	9,355	15,077
Total current liabilities	61,030	78,325
Deferred credits and other liabilities
Operating lease liabilities	1,513
Deferred income taxes	53,967	54,936
Regulatory liabilities	177,240	176,101
Unamortized tax credits	16,366	16,217
Defined benefit pension and other postretirement benefit plans liability	72,991	73,147
Other	34,765	32,319
Total deferred credits and other liabilities	356,842	352,720
Total liabilities and shareholders’ equity	941,144	951,668
Maui Electric | Reportable Legal Entities
Utility property, plant and equipment
Land	3,612	3,612
Plant and equipment	1,107,173	1,094,028
Less accumulated depreciation	(511,881)	(505,633)
Construction in progress	32,398	30,687
Utility property, plant and equipment, net	631,302	622,694
Nonutility property, plant and equipment, less accumulated depreciation	1,532	1,532
Total property, plant and equipment, net	632,834	624,226
Investment in wholly owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	1,461	3,421	6,230	6,332
Advances to affiliates	0
Customer accounts receivable, net	19,551	25,453
Accrued unbilled revenues, net	13,192	16,627
Other accounts receivable, net	1,967	3,033
Fuel oil stock, at average cost	14,612	14,646
Materials and supplies, at average cost	17,781	17,758
Prepayments and other	4,003	3,692
Regulatory assets	8,651	7,746
Total current assets	81,218	92,376
Other long-term assets
Operating lease right-of-use assets	410
Regulatory assets	105,429	104,044
Other	16,618	17,299
Total other long-term assets	122,457	121,343
Total assets	836,509	837,945
Capitalization
Total shareholders’ equity	283,776	280,863	270,483	270,265
Cumulative preferred stock—not subject to mandatory redemption	5,000	5,000
Long-term debt, net	180,957	200,916
Total capitalization	469,733	486,779
Current liabilities
Current portion of operating lease liabilities	29
Current portion of long-term debt	19,989
Short-term borrowings from non-affiliates	0	0
Short-term borrowings from affiliate	9,500
Accounts payable	21,389	25,362
Interest and preferred dividends payable	3,929	2,841
Taxes accrued	28,907	34,458
Regulatory liabilities	4,750	5,406
Other	14,493	20,414
Total current liabilities	102,986	88,481
Deferred credits and other liabilities
Operating lease liabilities	382
Deferred income taxes	57,607	56,823
Regulatory liabilities	99,137	98,948
Unamortized tax credits	14,880	15,034
Defined benefit pension and other postretirement benefit plans liability	71,304	71,338
Other	20,480	20,542
Total deferred credits and other liabilities	263,790	262,685
Total liabilities and shareholders’ equity	836,509	837,945
Other subsidiaries | Reportable Legal Entities
Utility property, plant and equipment
Land	0	0
Plant and equipment	0	0
Less accumulated depreciation	0	0
Construction in progress	0	0
Utility property, plant and equipment, net	0	0
Nonutility property, plant and equipment, less accumulated depreciation	0	0
Total property, plant and equipment, net	0	0
Investment in wholly owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	101	101	101	101
Advances to affiliates	0
Customer accounts receivable, net	0	0
Accrued unbilled revenues, net	0	0
Other accounts receivable, net	0	0
Fuel oil stock, at average cost	0	0
Materials and supplies, at average cost	0	0
Prepayments and other	0	0
Regulatory assets	0	0
Total current assets	101	101
Other long-term assets
Operating lease right-of-use assets	0
Regulatory assets	0	0
Other	0	0
Total other long-term assets	0	0
Total assets	101	101
Capitalization
Total shareholders’ equity	101	101	101	101
Cumulative preferred stock—not subject to mandatory redemption	0	0
Long-term debt, net	0	0
Total capitalization	101	101
Current liabilities
Current portion of operating lease liabilities	0
Current portion of long-term debt	0
Short-term borrowings from non-affiliates	0	0
Short-term borrowings from affiliate	0
Accounts payable	0	0
Interest and preferred dividends payable	0	0
Taxes accrued	0	0
Regulatory liabilities	0	0
Other	0	0
Total current liabilities	0	0
Deferred credits and other liabilities
Operating lease liabilities	0
Deferred income taxes	0	0
Regulatory liabilities	0	0
Unamortized tax credits	0	0
Defined benefit pension and other postretirement benefit plans liability	0	0
Other	0	0
Total deferred credits and other liabilities	0	0
Total liabilities and shareholders’ equity	101	101
Hawaiian Electric Company, Inc. and Subsidiaries
Utility property, plant and equipment
Land	49,667	49,667
Plant and equipment	6,874,568	6,809,671
Less accumulated depreciation	(2,615,214)	(2,577,342)
Construction in progress	247,317	233,145
Utility property, plant and equipment, net	4,556,338	4,515,141
Nonutility property, plant and equipment, less accumulated depreciation	6,960	6,961
Total property, plant and equipment, net	4,563,298	4,522,102
Investment in wholly owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	8,381	35,877	23,399	12,517
Advances to affiliates	0
Customer accounts receivable, net	137,413	177,896
Accrued unbilled revenues, net	95,905	121,738
Other accounts receivable, net	7,253	6,215
Fuel oil stock, at average cost	116,498	79,935
Materials and supplies, at average cost	56,584	55,204
Prepayments and other	33,887	32,118
Regulatory assets	72,018	71,016
Total current assets	527,939	579,999
Other long-term assets
Operating lease right-of-use assets	221,261	0
Regulatory assets	754,168	762,410
Other	104,222	102,992
Total other long-term assets	1,079,651	865,402
Total assets	6,170,888	5,967,503
Capitalization
Total shareholders’ equity	1,964,478	1,957,641	$ 1,846,955	$ 1,845,283
Cumulative preferred stock—not subject to mandatory redemption	34,293	34,293
Long-term debt, net	1,337,016	1,418,802
Total capitalization	3,335,787	3,410,736
Current liabilities
Current portion of operating lease liabilities	61,269	0
Current portion of long-term debt	81,957	0
Short-term borrowings from non-affiliates	55,999	25,000
Short-term borrowings from affiliate	0
Accounts payable	156,146	171,791
Interest and preferred dividends payable	27,608	23,215
Taxes accrued	193,334	233,333
Regulatory liabilities	12,613	17,977
Other	62,423	60,003
Total current liabilities	651,349	531,319
Deferred credits and other liabilities
Operating lease liabilities	159,875	0
Deferred income taxes	382,672	383,197
Regulatory liabilities	940,606	932,259
Unamortized tax credits	91,569	91,522
Defined benefit pension and other postretirement benefit plans liability	503,404	503,659
Other	105,626	114,811
Total deferred credits and other liabilities	2,183,752	2,025,448
Total liabilities and shareholders’ equity	$ 6,170,888	$ 5,967,503