Shareholders' equity - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	$ 1,927,640	$ 1,790,573	$ 1,726,406
Other comprehensive income (loss), net of tax benefits	(6,867)	1,116	(10,628)
Ending Balance	2,066,753	1,927,640	1,790,573
AOCI Including Portion Attributable to Noncontrolling Interest
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	(26,262)	(27,378)	(16,750)
Ending Balance	(33,129)	(26,262)	(27,378)
Net unrealized gains (losses) on securities
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	(1,872)	462	(3,663)
Other comprehensive income (loss), net of tax benefits	(6,059)	(2,334)	4,125
Ending Balance	(7,931)	(1,872)	462
Unrealized gains(losses) on derivatives
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	(54)	(289)	(525)
Other comprehensive income (loss), net of tax benefits	(400)	235	236
Ending Balance	(454)	(54)	(289)
Retirement benefit plans
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	(24,336)	(27,551)	(12,562)
Other comprehensive income (loss), net of tax benefits	(408)	3,215	(14,989)
Ending Balance	(24,744)	(24,336)	(27,551)
Hawaiian Electric Company, Inc. and Subsidiaries
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	1,728,325	1,682,144	1,593,564
Other comprehensive income (loss), net of tax benefits	(1,247)	880	(563)
Ending Balance	1,799,787	1,728,325	1,682,144
Hawaiian Electric Company, Inc. and Subsidiaries \| AOCI Including Portion Attributable to Noncontrolling Interest
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	925	45	608
Ending Balance	(322)	925	45
Hawaiian Electric Company, Inc. and Subsidiaries \| Unrealized gains(losses) on derivatives
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	0	0	0
Other comprehensive income (loss), net of tax benefits	(454)	0	0
Ending Balance	(454)	0	0
Hawaiian Electric Company, Inc. and Subsidiaries \| Retirement benefit plans
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	925	45	608
Other comprehensive income (loss), net of tax benefits	(793)	880	(563)
Ending Balance	$ 132	$ 925	$ 45