Segment financial information (Details) $ in Thousands			1 Months Ended	12 Months Ended
	Feb. 02, 2018 MWh MW	Nov. 24, 2017 MW	Sep. 30, 2020 a MW	Dec. 31, 2021 USD ($) MWh MW	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Segment financial information
Revenues				$ 2,850,379	$ 2,579,775	$ 2,873,948
Depreciation and amortization				278,702	290,778	278,113
Interest expense, net				99,403	99,808	109,339
Income (loss) before income taxes				310,863	240,624	271,409
Income taxes (benefit)				62,807	40,910	51,637
Net income (loss)				248,056	199,714	219,772
Preferred stock dividends of subsidiaries				1,890	1,890	1,890
Net income for common stock				246,166	197,824	217,882
Capital expenditures				314,524	383,895	457,520
Assets				15,822,637	15,004,007	13,745,251
Electric utility
Segment financial information
Revenues				2,539,636	2,265,320	2,545,942
Depreciation and amortization				251,206	256,479	245,362
Interest expense, net				72,447	67,794	70,842
Income (loss) before income taxes				223,785	211,753	197,140
Income taxes (benefit)				44,148	40,418	38,305
Net income (loss)				179,637	171,335	158,835
Preferred stock dividends of subsidiaries				1,995	1,995	1,995
Net income for common stock				177,642	169,340	156,840
Capital expenditures				292,000	350,864	419,898
Assets				6,491,625	6,457,373	6,388,682
Bank
Segment financial information
Revenues				306,398	313,511	327,917
Depreciation and amortization				21,124	29,349	28,675
Interest expense, net				5,040	11,114	18,440
Income (loss) before income taxes				130,559	69,271	112,034
Income taxes (benefit)				29,325	11,688	23,061
Net income (loss)				101,234	57,583	88,973
Preferred stock dividends of subsidiaries				0	0	0
Net income for common stock				101,234	57,583	88,973
Capital expenditures				11,131	12,203	24,175
Assets				9,181,603	8,396,533	7,233,017
Other
Segment financial information
Revenues				4,345	944	89
Depreciation and amortization				6,372	4,950	4,076
Interest expense, net				21,916	20,900	20,057
Income (loss) before income taxes				(43,481)	(40,400)	(37,765)
Income taxes (benefit)				(10,666)	(11,196)	(9,729)
Net income (loss)				(32,815)	(29,204)	(28,036)
Preferred stock dividends of subsidiaries				(105)	(105)	(105)
Net income for common stock				(32,710)	(29,099)	(27,931)
Capital expenditures				11,393	20,828	13,447
Assets				149,409	150,101	123,552
Operating Segments
Segment financial information
Revenues				2,850,379	2,579,775	2,873,948
Operating Segments | Electric utility
Segment financial information
Revenues				2,539,589	2,265,281	2,545,865
Operating Segments | Bank
Segment financial information
Revenues				306,398	313,511	327,917
Operating Segments | Other
Segment financial information
Revenues				4,392	983	166
Intersegment eliminations
Segment financial information
Revenues				0	0	0
Intersegment eliminations | Electric utility
Segment financial information
Revenues				47	39	77
Intersegment eliminations | Bank
Segment financial information
Revenues				0	0	0
Intersegment eliminations | Other
Segment financial information
Revenues				$ (47)	$ (39)	$ (77)
Hamakua Energy
Segment financial information
Power produced by power plants (in megawatts) | MW		60		60
Mauo, LLC
Segment financial information
Power produced by power plants (in megawatts) | MW	8.6			8.6
Power storage capacity (in megawatt hours) | MWh	42.3			42.3
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