Shareholders' equity - Accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			$ 1,927,640	$ 1,790,573
Current period other comprehensive income	$ (1,669)	$ 4,430	9,239	5,361
Ending Balance	2,068,388	1,921,001	2,068,388	1,921,001
AOCI Attributable to Parent [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(26,262)	(27,378)
Current period other comprehensive income			9,239	5,361
Ending Balance	(17,023)	(22,017)	(17,023)	(22,017)
Net unrealized gains (losses) on securities
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(1,872)	462
Current period other comprehensive income			7,837	3,608
Ending Balance	5,965	4,070	5,965	4,070
Unrealized gains (losses) on derivatives
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(54)	(289)
Current period other comprehensive income			459	177
Ending Balance	405	(112)	405	(112)
Retirement benefit plans
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(24,336)	(27,551)
Current period other comprehensive income			943	1,576
Ending Balance	(23,393)	(25,975)	(23,393)	(25,975)
Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			1,728,325	1,682,144
Current period other comprehensive income	151	4	412	11
Ending Balance	1,766,727	1,717,064	1,766,727	1,717,064
Hawaiian Electric Company, Inc. and Subsidiaries | AOCI Attributable to Parent [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			925	45
Current period other comprehensive income			412	11
Ending Balance	1,337	56	1,337	56
Hawaiian Electric Company, Inc. and Subsidiaries | Unrealized gains (losses) on derivatives
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			0	0
Current period other comprehensive income			405	0
Ending Balance	405	0	405	0
Hawaiian Electric Company, Inc. and Subsidiaries | Retirement benefit plans
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			925	45
Current period other comprehensive income			7	11
Ending Balance	$ 932	$ 56	$ 932	$ 56