Fair value measurements - Carrying or Notional Amount, Fair Value and Placement in the Fair Value Hierarchy of the Company’s Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Financial assets
Available-for-sale investment securities	$ 1,061,687	$ 1,136,439
Held-to-maturity investment securities	$ 1,058,691
Derivative asset, statement of financial position	Other	Other
Financial liabilities
Other bank borrowings	$ 520,000	$ 750,000
Derivative asset, statement of financial position		Other
Carrying or notional amount
Financial assets
Available-for-sale investment securities	1,061,687	$ 1,136,439
Held-to-maturity investment securities	1,179,182	1,201,314
Loans, net	5,977,249	6,121,606
Mortgage servicing rights	7,906	8,169
Derivative assets	41,122	16,880
Financial liabilities
Deposit liabilities - time certificates	1,048,825	1,063,907
Other bank borrowings	520,000	750,000
Long-term debt, net	2,838,224	2,842,429
Derivative liabilities		28,449
Carrying or notional amount | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,934,747	1,934,277
Estimated fair value
Financial assets
Available-for-sale investment securities	1,061,687	1,136,439
Held-to-maturity investment securities	1,058,691	1,103,668
Loans, net	5,508,465	5,738,999
Mortgage servicing rights	17,862	18,722
Derivative assets	1,822	1,058
Financial liabilities
Deposit liabilities - time certificates	1,037,878	1,053,101
Other bank borrowings	518,083	747,508
Long-term debt, net	2,124,907	2,133,225
Derivative liabilities		321
Estimated fair value | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,380,338	1,385,025
Estimated fair value | Quoted prices in active markets for identical assets (Level 1)
Financial assets
Available-for-sale investment securities	0	0
Held-to-maturity investment securities	0	0
Loans, net	0	0
Mortgage servicing rights	0	0
Derivative assets	5	0
Financial liabilities
Deposit liabilities - time certificates	0	0
Other bank borrowings	0	0
Long-term debt, net	0	0
Derivative liabilities		18
Estimated fair value | Quoted prices in active markets for identical assets (Level 1) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	0	0
Estimated fair value | Significant  other observable  inputs (Level 2)
Financial assets
Available-for-sale investment securities	1,047,611	1,122,081
Held-to-maturity investment securities	1,058,691	1,103,668
Loans, net	13,899	15,176
Mortgage servicing rights	0	0
Derivative assets	1,817	1,058
Financial liabilities
Deposit liabilities - time certificates	1,037,878	1,053,101
Other bank borrowings	518,083	747,508
Long-term debt, net	2,124,907	2,133,225
Derivative liabilities		303
Estimated fair value | Significant  other observable  inputs (Level 2) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,380,338	1,385,025
Estimated fair value | Significant unobservable inputs (Level 3)
Financial assets
Available-for-sale investment securities	14,076	14,358
Held-to-maturity investment securities	0	0
Loans, net	5,494,566	5,723,823
Mortgage servicing rights	17,862	18,722
Derivative assets	0	0
Financial liabilities
Deposit liabilities - time certificates	0	0
Other bank borrowings	0	0
Long-term debt, net	0	0
Derivative liabilities		0
Estimated fair value | Significant unobservable inputs (Level 3) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	$ 0	$ 0