Shareholders' equity - Reclassification Out Of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Revenues	$ 761,650	$ 768,048	$ 685,277	$ 645,874	$ 658,597	$ 673,185	$ 632,281	$ 591,562	$ 2,860,849	$ 2,555,625	$ 2,380,654
Total reclassifications									29,340	(62,533)	42,623
Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Revenues	$ 680,563	$ 687,409	$ 608,126	$ 570,427	$ 583,311	$ 598,769	$ 556,875	$ 518,611	2,546,525	2,257,566
Total reclassifications									27,337	(63,793)	41,665
Bank
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Revenues									314,275	297,640	285,924
Electric utility
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Revenues									2,546,525	2,257,566	2,094,368
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications									21,015	15,737	14,518
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent | Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications									19,012	14,477	13,254
Accumulated Defined Benefit Plans Adjustment, Impact Of Decision And Orders Of The Public Utility Commission Included In Regulatory Assets
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications									8,325	(78,724)	28,584
Accumulated Defined Benefit Plans Adjustment, Impact Of Decision And Orders Of The Public Utility Commission Included In Regulatory Assets | Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications									8,325	(78,724)	28,584
Amount reclassified from AOCI | Net unrealized gains (losses) on securities | Bank
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Revenues									0	0	360
Amount reclassified from AOCI | Unrealized gains (losses) on derivatives | Window forward contracts | Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications									0	454	(173)
Amount reclassified from AOCI | Unrealized gains (losses) on derivatives | Interest rate contracts
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications									0	0	54
Amount reclassified from AOCI | Unrealized gains (losses) on derivatives | Electric utility | Window forward contracts
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications									$ 0	$ 454	$ (173)