Electric utility segment - Condensed consolidating balance sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Utility property, plant and equipment
Total property, plant and equipment, net	$ 4,542,558	$ 4,460,248
Current assets
Cash and cash equivalents	244,785	261,881	$ 234,230	$ 278,452
Other long-term assets
Total assets	12,702,718	12,534,160
Capitalization
Common stock equity	2,091,777	2,097,386	2,065,588	2,066,753
Cumulative preferred stock—not subject to mandatory redemption	0	0
Current liabilities
Interest and preferred dividends payable	29,786	25,837
Deferred credits and other liabilities
Total liabilities and shareholders’ equity	12,702,718	12,534,160
Hawaiian Electric Company
Utility property, plant and equipment
Land	44,001	43,972
Plant and equipment	4,176,161	4,140,892
Less accumulated depreciation	(1,472,313)	(1,451,612)
Construction in progress	256,058	231,571
Utility property, plant and equipment, net	3,003,907	2,964,823
Nonutility property, plant and equipment, less accumulated depreciation	5,935	5,933
Total property, plant and equipment, net	3,009,842	2,970,756
Investment in wholly owned subsidiaries, at equity	559,511	557,013
Current assets
Cash and cash equivalents	11,988	2,059	8,617	61,388
Advances to affiliates	3,000	0
Customer accounts receivable, net	97,943	86,987
Accrued unbilled revenues, net	70,618	77,176
Other accounts receivable, net	10,019	11,376
Fuel oil stock, at average cost	66,294	64,972
Materials and supplies, at average cost	29,420	28,325
Prepayments and other	22,811	17,928
Regulatory assets	87,449	76,203
Total current assets	399,542	365,026
Other long-term assets
Regulatory assets	549,020	557,464
Other	63,792	60,157
Total other long-term assets	612,812	617,621
Total assets	4,581,707	4,510,416
Capitalization
Common stock equity	1,846,955	1,845,283	1,799,769	1,799,787
Cumulative preferred stock—not subject to mandatory redemption	22,293	22,293
Long-term debt, net	925,065	924,979
Total capitalization	2,794,313	2,792,555
Current liabilities
Current portion of long-term debt	29,984	29,978
Short-term borrowings from non-affiliates	121,983	4,999
Short-term borrowings from affiliate	0	12,000
Accounts payable	102,402	121,328
Interest and preferred dividends payable	18,422	15,677
Taxes accrued, including revenue taxes	107,968	133,839
Regulatory liabilities	2,612	607
Other	45,137	43,121
Total current liabilities	428,508	361,549
Deferred credits and other liabilities
Deferred income taxes	281,581	281,223
Regulatory liabilities	620,758	613,329
Unamortized tax credits	60,318	59,039
Defined benefit pension and other postretirement benefit plans liability	335,674	340,983
Other	60,555	61,738
Total deferred credits and other liabilities	1,358,886	1,356,312
Total liabilities and shareholders’ equity	4,581,707	4,510,416
HELCO
Utility property, plant and equipment
Land	5,923	6,189
Plant and equipment	1,212,692	1,206,776
Less accumulated depreciation	(534,083)	(528,024)
Construction in progress	10,150	8,182
Utility property, plant and equipment, net	694,682	693,123
Nonutility property, plant and equipment, less accumulated depreciation	115	115
Total property, plant and equipment, net	694,797	693,238
Investment in wholly owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	5,080	4,025	2,952	10,749
Advances to affiliates	0	0
Customer accounts receivable, net	24,117	22,510
Accrued unbilled revenues, net	15,182	15,940
Other accounts receivable, net	1,973	2,268
Fuel oil stock, at average cost	9,501	8,698
Materials and supplies, at average cost	8,591	8,041
Prepayments and other	3,661	4,514
Regulatory assets	6,698	5,038
Total current assets	74,803	71,034
Other long-term assets
Regulatory assets	120,529	122,783
Other	17,751	16,311
Total other long-term assets	138,280	139,094
Total assets	907,880	903,366
Capitalization
Common stock equity	288,927	286,647	292,001	291,291
Cumulative preferred stock—not subject to mandatory redemption	7,000	7,000
Long-term debt, net	202,725	202,701
Total capitalization	498,652	496,348
Current liabilities
Current portion of long-term debt	10,994	10,992
Short-term borrowings from non-affiliates	0	0
Short-term borrowings from affiliate	3,000	0
Accounts payable	17,867	17,855
Interest and preferred dividends payable	4,006	4,174
Taxes accrued, including revenue taxes	33,213	34,950
Regulatory liabilities	2,387	1,245
Other	9,127	9,818
Total current liabilities	80,594	79,034
Deferred credits and other liabilities
Deferred income taxes	55,093	56,955
Regulatory liabilities	172,193	169,139
Unamortized tax credits	16,315	16,167
Defined benefit pension and other postretirement benefit plans liability	65,340	66,447
Other	19,693	19,276
Total deferred credits and other liabilities	328,634	327,984
Total liabilities and shareholders’ equity	907,880	903,366
Maui Electric
Utility property, plant and equipment
Land	3,016	3,016
Plant and equipment	1,063,362	1,053,372
Less accumulated depreciation	(501,546)	(496,716)
Construction in progress	25,729	23,341
Utility property, plant and equipment, net	590,561	583,013
Nonutility property, plant and equipment, less accumulated depreciation	1,532	1,532
Total property, plant and equipment, net	592,093	584,545
Investment in wholly owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	6,230	6,332	1,537	2,048
Advances to affiliates	0	12,000
Customer accounts receivable, net	19,373	18,392
Accrued unbilled revenues, net	13,835	13,938
Other accounts receivable, net	1,314	1,210
Fuel oil stock, at average cost	12,928	13,203
Materials and supplies, at average cost	17,681	18,031
Prepayments and other	3,736	2,913
Regulatory assets	8,653	7,149
Total current assets	83,750	93,168
Other long-term assets
Regulatory assets	100,150	100,660
Other	16,752	15,061
Total other long-term assets	116,902	115,721
Total assets	792,745	793,434
Capitalization
Common stock equity	270,483	270,265	260,586	259,554
Cumulative preferred stock—not subject to mandatory redemption	5,000	5,000
Long-term debt, net	190,864	190,836
Total capitalization	466,347	466,101
Current liabilities
Current portion of long-term debt	8,995	8,993
Short-term borrowings from non-affiliates	0	0
Short-term borrowings from affiliate	0	0
Accounts payable	22,130	20,427
Interest and preferred dividends payable	3,791	2,735
Taxes accrued, including revenue taxes	25,284	30,312
Regulatory liabilities	1,934	1,549
Other	14,949	14,197
Total current liabilities	77,083	78,213
Deferred credits and other liabilities
Deferred income taxes	56,415	55,863
Regulatory liabilities	95,209	94,901
Unamortized tax credits	15,303	15,163
Defined benefit pension and other postretirement benefit plans liability	64,612	65,518
Other	17,776	17,675
Total deferred credits and other liabilities	249,315	249,120
Total liabilities and shareholders’ equity	792,745	793,434
Other subsidiaries
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	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
Regulatory assets	0	0
Other	0	0
Total other long-term assets	0	0
Total assets	101	101
Capitalization
Common stock 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 long-term debt	0	0
Short-term borrowings from non-affiliates	0	0
Short-term borrowings from affiliate	0	0
Accounts payable	0	0
Interest and preferred dividends payable	0	0
Taxes accrued, including revenue taxes	0	0
Regulatory liabilities	0	0
Other	0	0
Total current liabilities	0	0
Deferred credits and other liabilities
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
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	(559,511)	(557,013)
Current assets
Cash and cash equivalents	0	0	0	0
Advances to affiliates	(3,000)	(12,000)
Customer accounts receivable, net	0	0
Accrued unbilled revenues, net	0	0
Other accounts receivable, net	(9,353)	(7,691)
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	(12,353)	(19,691)
Other long-term assets
Regulatory assets	0	0
Other	0	0
Total other long-term assets	0	0
Total assets	(571,864)	(576,704)
Capitalization
Common stock equity	(559,511)	(557,013)	(552,688)	(550,946)
Cumulative preferred stock—not subject to mandatory redemption	0	0
Long-term debt, net	0	0
Total capitalization	(559,511)	(557,013)
Current liabilities
Current portion of long-term debt	0	0
Short-term borrowings from non-affiliates	0	0
Short-term borrowings from affiliate	(3,000)	(12,000)
Accounts payable	0	0
Interest and preferred dividends payable	(15)	(11)
Taxes accrued, including revenue taxes	0	0
Regulatory liabilities	0	0
Other	(9,338)	(7,680)
Total current liabilities	(12,353)	(19,691)
Deferred credits and other liabilities
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	(571,864)	(576,704)
Hawaiian Electric Company, Inc. and Subsidiaries
Utility property, plant and equipment
Land	52,940	53,177
Plant and equipment	6,452,215	6,401,040
Less accumulated depreciation	(2,507,942)	(2,476,352)
Construction in progress	291,937	263,094
Utility property, plant and equipment, net	4,289,150	4,240,959
Nonutility property, plant and equipment, less accumulated depreciation	7,582	7,580
Total property, plant and equipment, net	4,296,732	4,248,539
Investment in wholly owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	23,399	12,517	13,207	74,286
Advances to affiliates	0	0
Customer accounts receivable, net	141,433	127,889
Accrued unbilled revenues, net	99,635	107,054
Other accounts receivable, net	3,953	7,163
Fuel oil stock, at average cost	88,723	86,873
Materials and supplies, at average cost	55,692	54,397
Prepayments and other	30,208	25,355
Regulatory assets	102,800	88,390
Total current assets	545,843	509,638
Other long-term assets
Regulatory assets	769,699	780,907
Other	98,295	91,529
Total other long-term assets	867,994	872,436
Total assets	5,710,569	5,630,613
Capitalization
Common stock equity	1,846,955	1,845,283	$ 1,799,769	$ 1,799,787
Cumulative preferred stock—not subject to mandatory redemption	34,293	34,293
Long-term debt, net	1,318,654	1,318,516
Total capitalization	3,199,902	3,198,092
Current liabilities
Current portion of long-term debt	49,973	49,963
Short-term borrowings from non-affiliates	121,983	4,999
Short-term borrowings from affiliate	0	0
Accounts payable	142,399	159,610
Interest and preferred dividends payable	26,204	22,575
Taxes accrued, including revenue taxes	166,465	199,101
Regulatory liabilities	6,933	3,401
Other	59,875	59,456
Total current liabilities	573,832	499,105
Deferred credits and other liabilities
Deferred income taxes	393,089	394,041
Regulatory liabilities	888,160	877,369
Unamortized tax credits	91,936	90,369
Defined benefit pension and other postretirement benefit plans liability	465,626	472,948
Other	98,024	98,689
Total deferred credits and other liabilities	1,936,835	1,933,416
Total liabilities and shareholders’ equity	$ 5,710,569	$ 5,630,613