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	Mar. 31, 2024	Dec. 31, 2023
Financial assets
Available-for-sale investment securities	$ 1,091,889	$ 1,136,439
Held-to-maturity investment securities	$ 1,074,735
Derivative asset, statement of financial position	Other	Other
Financial liabilities
Other bank borrowings	$ 593,000	$ 750,000
Derivative asset, statement of financial position	Other	Other
Carrying or notional amount
Financial assets
Available-for-sale investment securities	$ 1,091,889	$ 1,136,439
Held-to-maturity investment securities	1,191,074	1,201,314
Loans, net	6,048,588	6,121,606
Mortgage servicing rights	8,050	8,169
Derivative assets	41,967	16,880
Financial liabilities
Deposit liabilities - time certificates	1,007,258	1,063,907
Other bank borrowings	593,000	750,000
Long-term debt, net	2,837,875	2,842,429
Derivative liabilities	6,250	28,449
Carrying or notional amount | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,932,959	1,934,277
Estimated fair value
Financial assets
Available-for-sale investment securities	1,091,889	1,136,439
Held-to-maturity investment securities	1,074,735	1,103,668
Loans, net	5,609,250	5,738,999
Mortgage servicing rights	18,430	18,722
Derivative assets	1,815	1,058
Financial liabilities
Deposit liabilities - time certificates	996,493	1,053,101
Other bank borrowings	591,244	747,508
Long-term debt, net	2,145,625	2,133,225
Derivative liabilities	14	321
Estimated fair value | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,392,483	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	0	0
Financial liabilities
Deposit liabilities - time certificates	0	0
Other bank borrowings	0	0
Long-term debt, net	0	0
Derivative liabilities	14	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	1,077,672	1,122,081
Held-to-maturity investment securities	1,074,735	1,103,668
Loans, net	2,922	15,176
Mortgage servicing rights	0	0
Derivative assets	1,815	1,058
Financial liabilities
Deposit liabilities - time certificates	996,493	1,053,101
Other bank borrowings	591,244	747,508
Long-term debt, net	2,145,625	2,133,225
Derivative liabilities	0	303
Estimated fair value | Significant  other observable  inputs (Level 2) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,392,483	1,385,025
Estimated fair value | Significant unobservable inputs (Level 3)
Financial assets
Available-for-sale investment securities	14,217	14,358
Held-to-maturity investment securities	0	0
Loans, net	5,606,328	5,723,823
Mortgage servicing rights	18,430	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