Electric utility segment - Condensed consolidating balance sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Utility property, plant and equipment
Total property, plant and equipment, net	$ 5,006,394			$ 4,830,118
Current assets
Cash and cash equivalents	176,988			169,208
Other long-term assets
Operating lease right-of-use assets	213,910
Total assets	13,517,970			13,104,051
Capitalization
Total shareholders’ equity	2,242,689	$ 2,208,586	$ 2,183,515	2,162,280	$ 2,132,045	$ 2,103,018	$ 2,091,777	$ 2,097,386
Cumulative preferred stock—not subject to mandatory redemption	0			0
Current liabilities
Interest and preferred dividends payable	32,338			28,254
Deferred credits and other liabilities
Deferred income taxes	393,140			372,518
Total liabilities and shareholders’ equity	13,517,970			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	(588,886)			(576,838)
Current assets
Cash and cash equivalents	0			0
Advances to affiliates	(37,200)
Customer accounts receivable, net	0			0
Accrued unbilled revenues, net	0			0
Other accounts receivable, net	(9,948)			(21,911)
Fuel oil stock, at average cost	0			0
Materials and supplies, at average cost	0			0
Prepayments and other	(1,395)			0
Regulatory assets	0			0
Total current assets	(48,543)			(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	(637,429)			(598,749)
Capitalization
Total shareholders’ equity	(588,886)			(576,838)	(571,574)			(557,013)
Cumulative preferred stock—not subject to mandatory redemption	0			0
Long-term debt, net	0			0
Total capitalization	(588,886)			(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	(37,200)
Accounts payable	0			0
Interest and preferred dividends payable	(69)			(32)
Taxes accrued	(1,395)			0
Regulatory liabilities	0			0
Other	(9,879)			(21,879)
Total current liabilities	(48,543)			(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	(637,429)			(598,749)
Hawaiian Electric (parent only) | Reportable Legal Entities
Utility property, plant and equipment
Land	42,112			40,449
Plant and equipment	4,676,163			4,456,090
Less accumulated depreciation	(1,595,962)			(1,523,861)
Construction in progress	185,022			193,677
Utility property, plant and equipment, net	3,307,335			3,166,355
Nonutility property, plant and equipment, less accumulated depreciation	5,311			5,314
Total property, plant and equipment, net	3,312,646			3,171,669
Investment in wholly owned subsidiaries, at equity	588,886			576,838
Current assets
Cash and cash equivalents	22,073			16,732
Advances to affiliates	22,200
Customer accounts receivable, net	111,171			125,960
Accrued unbilled revenues, net	90,015			88,060
Other accounts receivable, net	10,994			21,962
Fuel oil stock, at average cost	62,645			54,262
Materials and supplies, at average cost	33,747			30,291
Prepayments and other	38,439			23,214
Regulatory assets	29,410			60,093
Total current assets	420,694			420,574
Other long-term assets
Operating lease right-of-use assets	190,300
Regulatory assets	502,254			537,708
Other	72,386			69,749
Total other long-term assets	764,940			607,457
Total assets	5,087,166			4,776,538
Capitalization
Total shareholders’ equity	1,993,254			1,957,641	1,876,237			1,845,283
Cumulative preferred stock—not subject to mandatory redemption	22,293			22,293
Long-term debt, net	937,211			1,000,137
Total capitalization	2,952,758			2,980,071
Current liabilities
Current portion of operating lease liabilities	62,634
Current portion of long-term debt	61,976
Short-term borrowings from non-affiliates	112,353			25,000
Short-term borrowings from affiliate	15,000
Accounts payable	113,544			126,384
Interest and preferred dividends payable	19,699			16,203
Taxes accrued	143,156			164,747
Regulatory liabilities	9,255			7,699
Other	51,943			46,391
Total current liabilities	589,560			386,424
Deferred credits and other liabilities
Operating lease liabilities	126,979
Deferred income taxes	282,336			271,438
Regulatory liabilities	663,414			657,210
Unamortized tax credits	60,095			60,271
Defined benefit pension and other postretirement benefit plans liability	359,420			359,174
Other	52,604			61,950
Total deferred credits and other liabilities	1,544,848			1,410,043
Total liabilities and shareholders’ equity	5,087,166			4,776,538
HELCO | Reportable Legal Entities
Utility property, plant and equipment
Land	5,606			5,606
Plant and equipment	1,282,065			1,259,553
Less accumulated depreciation	(569,878)			(547,848)
Construction in progress	17,219			8,781
Utility property, plant and equipment, net	735,012			726,092
Nonutility property, plant and equipment, less accumulated depreciation	115			115
Total property, plant and equipment, net	735,127			726,207
Investment in wholly owned subsidiaries, at equity	0			0
Current assets
Cash and cash equivalents	5,003			15,623
Advances to affiliates	15,000
Customer accounts receivable, net	25,676			26,483
Accrued unbilled revenues, net	15,880			17,051
Other accounts receivable, net	1,516			3,131
Fuel oil stock, at average cost	10,694			11,027
Materials and supplies, at average cost	10,170			7,155
Prepayments and other	4,622			5,212
Regulatory assets	1,684			3,177
Total current assets	90,245			88,859
Other long-term assets
Operating lease right-of-use assets	1,560
Regulatory assets	112,900			120,658
Other	17,096			15,944
Total other long-term assets	131,556			136,602
Total assets	956,928			951,668
Capitalization
Total shareholders’ equity	303,345			295,874	294,220			286,647
Cumulative preferred stock—not subject to mandatory redemption	7,000			7,000
Long-term debt, net	203,952			217,749
Total capitalization	514,297			520,623
Current liabilities
Current portion of operating lease liabilities	94
Current portion of long-term debt	13,992
Short-term borrowings from non-affiliates	0			0
Short-term borrowings from affiliate	0
Accounts payable	17,654			20,045
Interest and preferred dividends payable	3,695			4,203
Taxes accrued	30,874			34,128
Regulatory liabilities	5,836			4,872
Other	10,187			15,077
Total current liabilities	82,332			78,325
Deferred credits and other liabilities
Operating lease liabilities	1,466
Deferred income taxes	53,939			54,936
Regulatory liabilities	181,472			176,101
Unamortized tax credits	16,054			16,217
Defined benefit pension and other postretirement benefit plans liability	71,112			73,147
Other	36,256			32,319
Total deferred credits and other liabilities	360,299			352,720
Total liabilities and shareholders’ equity	956,928			951,668
Maui Electric | Reportable Legal Entities
Utility property, plant and equipment
Land	3,612			3,612
Plant and equipment	1,139,058			1,094,028
Less accumulated depreciation	(520,548)			(505,633)
Construction in progress	24,315			30,687
Utility property, plant and equipment, net	646,437			622,694
Nonutility property, plant and equipment, less accumulated depreciation	1,532			1,532
Total property, plant and equipment, net	647,969			624,226
Investment in wholly owned subsidiaries, at equity	0			0
Current assets
Cash and cash equivalents	5,330			3,421
Advances to affiliates	0
Customer accounts receivable, net	26,246			25,453
Accrued unbilled revenues, net	17,925			16,627
Other accounts receivable, net	2,056			3,033
Fuel oil stock, at average cost	11,204			14,646
Materials and supplies, at average cost	16,893			17,758
Prepayments and other	4,655			3,692
Regulatory assets	1,857			7,746
Total current assets	86,166			92,376
Other long-term assets
Operating lease right-of-use assets	394
Regulatory assets	101,162			104,044
Other	18,511			17,299
Total other long-term assets	120,067			121,343
Total assets	854,202			837,945
Capitalization
Total shareholders’ equity	285,440			280,863	277,253			270,265
Cumulative preferred stock—not subject to mandatory redemption	5,000			5,000
Long-term debt, net	181,092			200,916
Total capitalization	471,532			486,779
Current liabilities
Current portion of operating lease liabilities	30
Current portion of long-term debt	19,997
Short-term borrowings from non-affiliates	0			0
Short-term borrowings from affiliate	22,200
Accounts payable	21,364			25,362
Interest and preferred dividends payable	4,215			2,841
Taxes accrued	32,204			34,458
Regulatory liabilities	4,425			5,406
Other	15,648			20,414
Total current liabilities	120,083			88,481
Deferred credits and other liabilities
Operating lease liabilities	367
Deferred income taxes	56,286			56,823
Regulatory liabilities	99,338			98,948
Unamortized tax credits	14,571			15,034
Defined benefit pension and other postretirement benefit plans liability	69,654			71,338
Other	22,371			20,542
Total deferred credits and other liabilities	262,587			262,685
Total liabilities and shareholders’ equity	854,202			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
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	51,330			49,667
Plant and equipment	7,097,286			6,809,671
Less accumulated depreciation	(2,686,388)			(2,577,342)
Construction in progress	226,556			233,145
Utility property, plant and equipment, net	4,688,784			4,515,141
Nonutility property, plant and equipment, less accumulated depreciation	6,958			6,961
Total property, plant and equipment, net	4,695,742			4,522,102
Investment in wholly owned subsidiaries, at equity	0			0
Current assets
Cash and cash equivalents	32,507			35,877
Advances to affiliates	0
Customer accounts receivable, net	163,093			177,896
Accrued unbilled revenues, net	123,820			121,738
Other accounts receivable, net	4,618			6,215
Fuel oil stock, at average cost	84,543			79,935
Materials and supplies, at average cost	60,810			55,204
Prepayments and other	46,321			32,118
Regulatory assets	32,951			71,016
Total current assets	548,663			579,999
Other long-term assets
Operating lease right-of-use assets	192,254
Regulatory assets	716,316			762,410
Other	107,993			102,992
Total other long-term assets	1,016,563			865,402
Total assets	6,260,968			5,967,503
Capitalization
Total shareholders’ equity	1,993,254	$ 1,971,762	$ 1,964,478	1,957,641	$ 1,876,237	$ 1,852,324	$ 1,846,955	$ 1,845,283
Cumulative preferred stock—not subject to mandatory redemption	34,293			34,293
Long-term debt, net	1,322,255			1,418,802
Total capitalization	3,349,802			3,410,736
Current liabilities
Current portion of operating lease liabilities	62,758			0
Current portion of long-term debt	95,965			0
Short-term borrowings from non-affiliates	112,353			25,000
Short-term borrowings from affiliate	0
Accounts payable	152,562			171,791
Interest and preferred dividends payable	27,540			23,215
Taxes accrued	204,839			233,333
Regulatory liabilities	19,516			17,977
Other	67,899			60,003
Total current liabilities	743,432			531,319
Deferred credits and other liabilities
Operating lease liabilities	128,812			0
Deferred income taxes	392,561			383,197
Regulatory liabilities	944,224			932,259
Unamortized tax credits	90,720			91,522
Defined benefit pension and other postretirement benefit plans liability	500,186			503,659
Other	111,231			114,811
Total deferred credits and other liabilities	2,167,734			2,025,448
Total liabilities and shareholders’ equity	$ 6,260,968			$ 5,967,503