Electric utility segment - Condensed consolidating balance sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Utility property, plant and equipment
Total property, plant and equipment, net	$ 4,932,245		$ 4,830,118
Current assets
Cash and cash equivalents	198,549		169,208
Other long-term assets
Operating lease right-of-use assets	226,157
Total assets	13,537,766		13,104,051
Capitalization
Total shareholders’ equity	2,208,586	$ 2,183,515	2,162,280	$ 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	28,373		28,254
Deferred credits and other liabilities
Deferred income taxes	380,233		372,518
Total liabilities and shareholders’ equity	13,537,766		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	(584,149)		(576,838)
Current assets
Cash and cash equivalents	0		0
Advances to affiliates	(30,300)
Customer accounts receivable, net	0		0
Accrued unbilled revenues, net	0		0
Other accounts receivable, net	(19,570)		(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	(49,870)		(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	(634,019)		(598,749)
Capitalization
Total shareholders’ equity	(584,149)	(582,374)	(576,838)	(561,764)	(559,511)	(557,013)
Cumulative preferred stock—not subject to mandatory redemption	0		0
Long-term debt, net	0		0
Total capitalization	(584,149)		(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	(30,300)
Accounts payable	0		0
Interest and preferred dividends payable	(81)		(32)
Taxes accrued	0		0
Regulatory liabilities	0		0
Other	(19,489)		(21,879)
Total current liabilities	(49,870)		(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	(634,019)		(598,749)
Hawaiian Electric (parent only) | Reportable Legal Entities
Utility property, plant and equipment
Land	42,183		40,449
Plant and equipment	4,558,178		4,456,090
Less accumulated depreciation	(1,573,545)		(1,523,861)
Construction in progress	222,328		193,677
Utility property, plant and equipment, net	3,249,144		3,166,355
Nonutility property, plant and equipment, less accumulated depreciation	5,312		5,314
Total property, plant and equipment, net	3,254,456		3,171,669
Investment in wholly owned subsidiaries, at equity	584,149		576,838
Current assets
Cash and cash equivalents	17,121		16,732
Advances to affiliates	25,300
Customer accounts receivable, net	109,401		125,960
Accrued unbilled revenues, net	86,291		88,060
Other accounts receivable, net	17,447		21,962
Fuel oil stock, at average cost	100,903		54,262
Materials and supplies, at average cost	33,874		30,291
Prepayments and other	23,804		23,214
Regulatory assets	46,673		60,093
Total current assets	460,814		420,574
Other long-term assets
Operating lease right-of-use assets	205,148
Regulatory assets	513,738		537,708
Other	74,994		69,749
Total other long-term assets	793,880		607,457
Total assets	5,093,299		4,776,538
Capitalization
Total shareholders’ equity	1,971,762	1,964,478	1,957,641	1,852,324	1,846,955	1,845,283
Cumulative preferred stock—not subject to mandatory redemption	22,293		22,293
Long-term debt, net	937,068		1,000,137
Total capitalization	2,931,123		2,980,071
Current liabilities
Current portion of operating lease liabilities	61,941
Current portion of long-term debt	61,946
Short-term borrowings from non-affiliates	161,901		25,000
Short-term borrowings from affiliate	5,000
Accounts payable	121,032		126,384
Interest and preferred dividends payable	16,287		16,203
Taxes accrued	127,413		164,747
Regulatory liabilities	5,687		7,699
Other	53,450		46,391
Total current liabilities	614,657		386,424
Deferred credits and other liabilities
Operating lease liabilities	142,905
Deferred income taxes	271,441		271,438
Regulatory liabilities	660,351		657,210
Unamortized tax credits	60,375		60,271
Defined benefit pension and other postretirement benefit plans liability	362,174		359,174
Other	50,273		61,950
Total deferred credits and other liabilities	1,547,519		1,410,043
Total liabilities and shareholders’ equity	5,093,299		4,776,538
HELCO | Reportable Legal Entities
Utility property, plant and equipment
Land	5,606		5,606
Plant and equipment	1,268,694		1,259,553
Less accumulated depreciation	(562,286)		(547,848)
Construction in progress	17,791		8,781
Utility property, plant and equipment, net	729,805		726,092
Nonutility property, plant and equipment, less accumulated depreciation	115		115
Total property, plant and equipment, net	729,920		726,207
Investment in wholly owned subsidiaries, at equity	0		0
Current assets
Cash and cash equivalents	3,352		15,623
Advances to affiliates	5,000
Customer accounts receivable, net	26,864		26,483
Accrued unbilled revenues, net	15,429		17,051
Other accounts receivable, net	8,526		3,131
Fuel oil stock, at average cost	11,376		11,027
Materials and supplies, at average cost	9,611		7,155
Prepayments and other	5,202		5,212
Regulatory assets	2,122		3,177
Total current assets	87,482		88,859
Other long-term assets
Operating lease right-of-use assets	1,582
Regulatory assets	115,178		120,658
Other	16,677		15,944
Total other long-term assets	133,437		136,602
Total assets	950,839		951,668
Capitalization
Total shareholders’ equity	300,619	298,497	295,874	288,865	288,927	286,647
Cumulative preferred stock—not subject to mandatory redemption	7,000		7,000
Long-term debt, net	217,845		217,749
Total capitalization	525,464		520,623
Current liabilities
Current portion of operating lease liabilities	92
Current portion of long-term debt	0
Short-term borrowings from non-affiliates	0		0
Short-term borrowings from affiliate	0
Accounts payable	15,059		20,045
Interest and preferred dividends payable	4,225		4,203
Taxes accrued	28,748		34,128
Regulatory liabilities	5,781		4,872
Other	14,842		15,077
Total current liabilities	68,747		78,325
Deferred credits and other liabilities
Operating lease liabilities	1,490
Deferred income taxes	53,564		54,936
Regulatory liabilities	178,018		176,101
Unamortized tax credits	16,514		16,217
Defined benefit pension and other postretirement benefit plans liability	71,830		73,147
Other	35,212		32,319
Total deferred credits and other liabilities	356,628		352,720
Total liabilities and shareholders’ equity	950,839		951,668
Maui Electric | Reportable Legal Entities
Utility property, plant and equipment
Land	3,612		3,612
Plant and equipment	1,112,171		1,094,028
Less accumulated depreciation	(514,379)		(505,633)
Construction in progress	35,193		30,687
Utility property, plant and equipment, net	636,597		622,694
Nonutility property, plant and equipment, less accumulated depreciation	1,532		1,532
Total property, plant and equipment, net	638,129		624,226
Investment in wholly owned subsidiaries, at equity	0		0
Current assets
Cash and cash equivalents	2,787		3,421
Advances to affiliates	0
Customer accounts receivable, net	25,824		25,453
Accrued unbilled revenues, net	17,428		16,627
Other accounts receivable, net	2,086		3,033
Fuel oil stock, at average cost	9,362		14,646
Materials and supplies, at average cost	17,609		17,758
Prepayments and other	2,980		3,692
Regulatory assets	6,830		7,746
Total current assets	84,906		92,376
Other long-term assets
Operating lease right-of-use assets	402
Regulatory assets	103,224		104,044
Other	16,965		17,299
Total other long-term assets	120,591		121,343
Total assets	843,626		837,945
Capitalization
Total shareholders’ equity	283,429	283,776	280,863	272,798	270,483	270,265
Cumulative preferred stock—not subject to mandatory redemption	5,000		5,000
Long-term debt, net	181,065		200,916
Total capitalization	469,494		486,779
Current liabilities
Current portion of operating lease liabilities	30
Current portion of long-term debt	19,993
Short-term borrowings from non-affiliates	0		0
Short-term borrowings from affiliate	25,300
Accounts payable	18,414		25,362
Interest and preferred dividends payable	2,914		2,841
Taxes accrued	27,305		34,458
Regulatory liabilities	3,485		5,406
Other	13,249		20,414
Total current liabilities	110,690		88,481
Deferred credits and other liabilities
Operating lease liabilities	374
Deferred income taxes	57,559		56,823
Regulatory liabilities	99,224		98,948
Unamortized tax credits	14,725		15,034
Defined benefit pension and other postretirement benefit plans liability	70,243		71,338
Other	21,317		20,542
Total deferred credits and other liabilities	263,442		262,685
Total liabilities and shareholders’ equity	843,626		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	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	51,401		49,667
Plant and equipment	6,939,043		6,809,671
Less accumulated depreciation	(2,650,210)		(2,577,342)
Construction in progress	275,312		233,145
Utility property, plant and equipment, net	4,615,546		4,515,141
Nonutility property, plant and equipment, less accumulated depreciation	6,959		6,961
Total property, plant and equipment, net	4,622,505		4,522,102
Investment in wholly owned subsidiaries, at equity	0		0
Current assets
Cash and cash equivalents	23,361		35,877
Advances to affiliates	0
Customer accounts receivable, net	162,089		177,896
Accrued unbilled revenues, net	119,148		121,738
Other accounts receivable, net	8,489		6,215
Fuel oil stock, at average cost	121,641		79,935
Materials and supplies, at average cost	61,094		55,204
Prepayments and other	31,986		32,118
Regulatory assets	55,625		71,016
Total current assets	583,433		579,999
Other long-term assets
Operating lease right-of-use assets	207,132
Regulatory assets	732,140		762,410
Other	108,636		102,992
Total other long-term assets	1,047,908		865,402
Total assets	6,253,846		5,967,503
Capitalization
Total shareholders’ equity	1,971,762	$ 1,964,478	1,957,641	$ 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	1,335,978		1,418,802
Total capitalization	3,342,033		3,410,736
Current liabilities
Current portion of operating lease liabilities	62,063		0
Current portion of long-term debt	81,939		0
Short-term borrowings from non-affiliates	161,901		25,000
Short-term borrowings from affiliate	0
Accounts payable	154,505		171,791
Interest and preferred dividends payable	23,345		23,215
Taxes accrued	183,466		233,333
Regulatory liabilities	14,953		17,977
Other	62,052		60,003
Total current liabilities	744,224		531,319
Deferred credits and other liabilities
Operating lease liabilities	144,769		0
Deferred income taxes	382,564		383,197
Regulatory liabilities	937,593		932,259
Unamortized tax credits	91,614		91,522
Defined benefit pension and other postretirement benefit plans liability	504,247		503,659
Other	106,802		114,811
Total deferred credits and other liabilities	2,167,589		2,025,448
Total liabilities and shareholders’ equity	$ 6,253,846		$ 5,967,503