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	Sep. 30, 2024	Dec. 31, 2023
Financial assets
Available-for-sale investment securities	$ 1,084,083	$ 1,136,439
Held-to-maturity investment securities	$ 1,086,205
Derivative asset, statement of financial position	Other	Other
Financial liabilities
Other bank borrowings	$ 520,000	$ 750,000
Derivative liabilities, statement of financial position	Other	Other
Carrying or notional amount
Financial assets
Available-for-sale investment securities	$ 1,084,083	$ 1,136,439
Held-to-maturity investment securities	1,159,229	1,201,314
Stock in Federal Home Loan Bank	29,204	14,728
Loans, net	5,975,318	6,121,606
Mortgage servicing rights	7,722	8,169
Derivative assets	16,991	16,880
Financial liabilities
Deposit liabilities - time certificates	1,064,978	1,063,907
Other bank borrowings	520,000	750,000
Long-term debt, net	2,836,539	2,842,429
Derivative liabilities	21,867	28,449
Carrying or notional amount | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,934,980	1,934,277
Estimated fair value
Financial assets
Available-for-sale investment securities	1,084,083	1,136,439
Held-to-maturity investment securities	1,086,205	1,103,668
Stock in Federal Home Loan Bank	29,204	14,728
Loans, net	5,672,330	5,738,999
Mortgage servicing rights	17,046	18,722
Derivative assets	802	1,058
Financial liabilities
Deposit liabilities - time certificates	1,058,464	1,053,101
Other bank borrowings	520,677	747,508
Long-term debt, net	2,289,207	2,133,225
Derivative liabilities	116	321
Estimated fair value | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,519,620	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
Stock in Federal Home Loan Bank	0	0
Loans, net	0	0
Mortgage servicing rights	0	0
Derivative assets	10	0
Financial liabilities
Deposit liabilities - time certificates	0	0
Other bank borrowings	0	0
Long-term debt, net	0	0
Derivative liabilities	0	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	1,070,148	1,122,081
Held-to-maturity investment securities	1,086,205	1,103,668
Stock in Federal Home Loan Bank	29,204	14,728
Loans, net	2,698	15,176
Mortgage servicing rights	0	0
Derivative assets	792	1,058
Financial liabilities
Deposit liabilities - time certificates	1,058,464	1,053,101
Other bank borrowings	520,677	747,508
Long-term debt, net	2,289,207	2,133,225
Derivative liabilities	116	303
Estimated fair value | Significant  other observable  inputs (Level 2) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,519,620	1,385,025
Estimated fair value | Significant unobservable inputs (Level 3)
Financial assets
Available-for-sale investment securities	13,935	14,358
Held-to-maturity investment securities	0	0
Stock in Federal Home Loan Bank	0	0
Loans, net	5,669,632	5,723,823
Mortgage servicing rights	17,046	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	0
Estimated fair value | Significant unobservable inputs (Level 3) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	$ 0	$ 0