Shareholders' equity - Accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			$ 2,066,753	$ 1,927,640
Current period other comprehensive income	$ 2,370	$ 2,108	3,355	10,908
Ending Balance	2,075,029	1,966,182	2,075,029	1,966,182
AOCI
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(33,129)	(26,262)
Current period other comprehensive income			3,355	10,908
Ending Balance	(29,774)	(15,354)	(29,774)	(15,354)
Net unrealized gains (losses) on securities
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(7,931)	(1,872)
Current period other comprehensive income			2,244	9,984
Ending Balance	(5,687)	8,112	(5,687)	8,112
Unrealized gains (losses) on derivatives
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(454)	(54)
Current period other comprehensive income			454	311
Ending Balance	0	257	0	257
Retirement benefit plans
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(24,744)	(24,336)
Current period other comprehensive income			657	613
Ending Balance	(24,087)	(23,723)	(24,087)	(23,723)
Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			1,799,787	1,728,325
Current period other comprehensive income	40	(755)	499	261
Ending Balance	1,803,506	1,743,006	1,803,506	1,743,006
Hawaiian Electric Company, Inc. and Subsidiaries | AOCI
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(322)	925
Current period other comprehensive income			499	261
Ending Balance	177	1,186	177	1,186
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			(454)	0
Current period other comprehensive income			454	257
Ending Balance	0	257	0	257
Hawaiian Electric Company, Inc. and Subsidiaries | Retirement benefit plans
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			132	925
Current period other comprehensive income			45	4
Ending Balance	$ 177	$ 929	$ 177	$ 929