Segment financial information (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2020 a MW	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2018 MWh MW	Dec. 31, 2017 MW	Jul. 31, 2022 MW	Jul. 01, 2022 MW
Segment financial information
Revenues		$ 3,741,985	$ 2,850,379	$ 2,579,775
Depreciation and amortization		294,841	278,702	290,778
Interest expense, net		116,703	99,403	99,808
Income before income taxes		304,195	310,863	240,624
Income taxes (benefit)		61,167	62,807	40,910
Net income		243,028	248,056	199,714
Preferred stock dividends of subsidiaries		1,890	1,890	1,890
Net income for common stock		241,138	246,166	197,824
Capital expenditures		344,037	314,524	383,895
Assets		16,284,244	15,822,637	15,004,007
Electric utility
Segment financial information
Revenues		3,408,587	2,539,636	2,265,320
Depreciation and amortization		260,744	251,206	256,479
Interest expense, net		76,416	72,447	67,794
Income before income taxes		240,600	223,785	211,753
Income taxes (benefit)		49,676	44,148	40,418
Net income		190,924	179,637	171,335
Preferred stock dividends of subsidiaries		1,995	1,995	1,995
Net income for common stock		188,929	177,642	169,340
Capital expenditures		329,457	292,000	350,864
Assets		6,597,467	6,491,625	6,457,373
Bank
Segment financial information
Revenues		321,068	306,398	313,511
Depreciation and amortization		24,436	21,124	29,349
Interest expense, net		13,301	5,040	11,114
Income before income taxes		102,241	130,559	69,271
Income taxes (benefit)		22,252	29,325	11,688
Net income		79,989	101,234	57,583
Preferred stock dividends of subsidiaries		0	0	0
Net income for common stock		79,989	101,234	57,583
Capital expenditures		4,704	11,131	12,203
Assets		9,545,970	9,181,603	8,396,533
Other
Segment financial information
Revenues		12,330	4,345	944
Depreciation and amortization		9,661	6,372	4,950
Interest expense, net		26,986	21,916	20,900
Income before income taxes		(38,646)	(43,481)	(40,400)
Income taxes (benefit)		(10,761)	(10,666)	(11,196)
Net income		(27,885)	(32,815)	(29,204)
Preferred stock dividends of subsidiaries		(105)	(105)	(105)
Net income for common stock		(27,780)	(32,710)	(29,099)
Capital expenditures		9,876	11,393	20,828
Assets		140,807	149,409	150,101
Operating Segments
Segment financial information
Revenues		3,741,985	2,850,379	2,579,775
Operating Segments | Electric utility
Segment financial information
Revenues		3,408,583	2,539,589	2,265,281
Operating Segments | Bank
Segment financial information
Revenues		321,068	306,398	313,511
Operating Segments | Other
Segment financial information
Revenues		12,334	4,392	983
Intersegment eliminations
Segment financial information
Revenues		0	0	0
Intersegment eliminations | Electric utility
Segment financial information
Revenues		4	47	39
Intersegment eliminations | Bank
Segment financial information
Revenues		0	0	0
Intersegment eliminations | Other
Segment financial information
Revenues		$ (4)	$ (47)	$ (39)
Hamakua Energy
Segment financial information
Power produced by power plants (in megawatts) | MW						60
Mauo, LLC
Segment financial information
Power produced by power plants (in megawatts) | MW					8.1
Power storage capacity (in megawatt hours) | MWh					42.6
Power purchase agreement term					15 years
Power purchase agreement extension term					5 years
Ka‘ie‘ie Waho Company, LLC
Segment financial information
Photovoltaic system power amount (in megawatts) | MW	6
Area of land (in acres) | a	20
Mahipapa, LLC | Green Energy Team, LLC
Segment financial information
Unit of renewable energy (in mega watts) | MW							7.5	7.5