Fair value measurements - Summary of financial assets and liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financial assets
Available-for-sale investment securities	$ 894,021	$ 820,648
Financial liabilities
Short-term borrowings—other than bank	115,985	103,063
Other bank borrowings	272,887	328,582
Carrying or notional amount
Financial assets
Money market funds	10	10
Available-for-sale investment securities	894,021	820,648
Stock in Federal Home Loan Bank	11,218	10,678
Loans receivable, net	4,705,840	4,570,412
Mortgage-servicing rights	9,016	8,884
Bank-owned life insurance	140,176	138,139
Derivative assets	55,879	22,616
Financial liabilities
Deposit liabilities	5,232,203	5,025,254
Short-term borrowings—other than bank	115,985	103,063
Other bank borrowings	272,887	328,582
Long-term debt, net—other than bank	1,578,842	1,578,368
Derivative liabilities	30,263	23,269
Carrying or notional amount | Hawaiian Electric Company, Inc. and Subsidiaries
Financial assets
Derivative assets	20,637
Financial liabilities
The Utilities’ short-term borrowings (included in amount above)	36,995
Long-term debt, net—other than bank	1,279,123	1,278,702
Estimated fair value
Financial assets
Money market funds	10	10
Available-for-sale investment securities	894,021	820,648
Stock in Federal Home Loan Bank	11,218	10,678
Loans receivable, net	4,940,177	4,749,525
Mortgage-servicing rights	11,224	11,790
Bank-owned life insurance	140,176	138,139
Derivative assets	1,219	385
Financial liabilities
Deposit liabilities	5,238,391	5,024,500
Short-term borrowings—other than bank	115,985	103,063
Other bank borrowings	276,709	333,392
Long-term debt, net—other than bank	1,749,242	1,669,087
Derivative liabilities	270	30
Estimated fair value | Hawaiian Electric Company, Inc. and Subsidiaries
Financial assets
Derivative assets	420
Financial liabilities
The Utilities’ short-term borrowings (included in amount above)	36,995
Long-term debt, net—other than bank	1,441,061	1,363,766
Estimated fair value | Level 1
Financial assets
Derivative assets	0	0
Financial liabilities
Derivative liabilities	211	15
Estimated fair value | Level 2
Financial assets
Money market funds	10	10
Available-for-sale investment securities	894,021	820,648
Stock in Federal Home Loan Bank	11,218	10,678
Loans receivable, net	6,242	4,639
Bank-owned life insurance	140,176	138,139
Derivative assets	1,219	385
Financial liabilities
Deposit liabilities	5,238,391	5,024,500
Short-term borrowings—other than bank	115,985	103,063
Other bank borrowings	276,709	333,392
Long-term debt, net—other than bank	1,749,242	1,669,087
Derivative liabilities	59	15
Estimated fair value | Level 2 | Hawaiian Electric Company, Inc. and Subsidiaries
Financial assets
Derivative assets	420
Financial liabilities
The Utilities’ short-term borrowings (included in amount above)	36,995
Long-term debt, net—other than bank	1,441,061	1,363,766
Estimated fair value | Level 3
Financial assets
Loans receivable, net	4,933,935	4,744,886
Mortgage-servicing rights	$ 11,224	$ 11,790