Fair value measurements - Summary of financial assets and liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Financial assets
Available-for-sale investment securities	$ 1,419,755	$ 1,429,667
Held-to-maturity investment securities	1,158,090
Financial liabilities
Short-term borrowings—other than bank	148,802	172,568
Other bank borrowings	680,690	695,120
Carrying or notional amount
Financial assets
Available-for-sale investment securities	1,419,755	1,429,667
Held-to-maturity investment securities	1,238,185	1,251,747
Loans, net	5,988,718	5,907,514
Mortgage-servicing rights	8,745	9,047
Derivative assets	38,050	16,220
Financial liabilities
Deposit liabilities	843,415	611,718
Short-term borrowings—other than bank	148,802	172,568
Other bank borrowings	680,690	695,120
Long-term debt, net	2,480,948	2,384,980
Derivative liabilities	250	22,949
Carrying or notional amount | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Short-term borrowings		87,967
Long-term debt, net	1,834,320	1,684,816
Estimated fair value
Financial assets
Available-for-sale investment securities	1,419,755	1,429,667
Held-to-maturity investment securities	1,158,090	1,150,971
Loans, net	5,606,360	5,454,202
Mortgage-servicing rights	18,117	17,646
Derivative assets	1,142	1,348
Financial liabilities
Deposit liabilities	829,709	597,617
Short-term borrowings—other than bank	148,802	172,568
Other bank borrowings	675,107	695,095
Long-term debt, net	2,296,948	2,122,605
Derivative liabilities	4	472
Estimated fair value | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Short-term borrowings		87,967
Long-term debt, net	1,702,247	1,487,496
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	9	18
Financial liabilities
Deposit liabilities	0	0
Short-term borrowings—other than bank	0	0
Other bank borrowings	0	0
Long-term debt, net	0	0
Derivative liabilities	4	0
Estimated fair value | Quoted prices in active markets for identical assets (Level 1) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Short-term borrowings		0
Long-term debt, net	0	0
Estimated fair value | Significant  other observable  inputs (Level 2)
Financial assets
Available-for-sale investment securities	1,404,989	1,414,765
Held-to-maturity investment securities	1,158,090	1,150,971
Loans, net	661	821
Mortgage-servicing rights	0	0
Derivative assets	1,133	1,330
Financial liabilities
Deposit liabilities	829,709	597,617
Short-term borrowings—other than bank	148,802	172,568
Other bank borrowings	675,107	695,095
Long-term debt, net	2,296,948	2,122,605
Derivative liabilities	0	472
Estimated fair value | Significant  other observable  inputs (Level 2) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Short-term borrowings		87,967
Long-term debt, net	1,702,247	1,487,496
Estimated fair value | Significant unobservable inputs (Level 3)
Financial assets
Available-for-sale investment securities	14,766	14,902
Held-to-maturity investment securities	0	0
Loans, net	5,605,699	5,453,381
Mortgage-servicing rights	18,117	17,646
Derivative assets	0	0
Financial liabilities
Deposit liabilities	0	0
Short-term borrowings—other than bank	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
Short-term borrowings		0
Long-term debt, net	$ 0	$ 0