Fair value measurements - Summary of financial assets and liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financial assets
Available-for-sale investment securities	$ 1,302,886	$ 1,105,182
Financial liabilities
Short-term borrowings—other than bank	49,789	0
Other bank borrowings	188,130	192,618
Carrying or notional amount
Financial assets
Money market funds		13,085
Available-for-sale investment securities	1,302,886	1,105,182
Stock in Federal Home Loan Bank	11,706	11,218
Loans receivable, net	4,693,539	4,701,977
Mortgage-servicing rights	9,181	9,373
Bank-owned life insurance	146,122	143,197
Derivative assets	58,120	23,578
Financial liabilities
Deposit liabilities	5,724,386	5,548,929
Short-term borrowings—other than bank	49,789	0
Other bank borrowings	188,130	192,618
Long-term debt, net	1,618,647	1,619,019
Derivative liabilities-window forward contracts	8,263	53,852
Carrying or notional amount | Hawaiian Electric Company, Inc. and Subsidiaries
Financial assets
Derivative assets	15,995
Financial liabilities
Short-term borrowings	43,990
Long-term debt, net	1,318,845	1,319,260
Derivative liabilities-window forward contracts	4,726	20,734
Estimated fair value
Financial assets
Money market funds		13,085
Available-for-sale investment securities	1,302,886	1,105,182
Stock in Federal Home Loan Bank	11,706	11,218
Loans receivable, net	4,842,065	4,852,826
Mortgage-servicing rights	12,270	13,216
Bank-owned life insurance	146,122	143,197
Derivative assets	845	453
Financial liabilities
Deposit liabilities	5,721,882	5,546,644
Short-term borrowings—other than bank	49,789	0
Other bank borrowings	188,513	193,991
Long-term debt, net	1,740,479	1,704,717
Derivative liabilities-window forward contracts	246	952
Estimated fair value | Hawaiian Electric Company, Inc. and Subsidiaries
Financial assets
Derivative assets	615
Financial liabilities
Short-term borrowings	43,990
Long-term debt, net	1,434,528	1,399,490
Derivative liabilities-window forward contracts	230	743
Estimated fair value | Level 1
Financial assets
Money market funds		0
Available-for-sale investment securities	0	0
Stock in Federal Home Loan Bank	0	0
Loans receivable, net	0	0
Mortgage-servicing rights	0	0
Bank-owned life insurance	0	0
Derivative assets	47	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-window forward contracts	0	129
Estimated fair value | Level 1 | Hawaiian Electric Company, Inc. and Subsidiaries
Financial assets
Derivative assets	0
Financial liabilities
Short-term borrowings	0
Long-term debt, net	0	0
Derivative liabilities-window forward contracts	0	0
Estimated fair value | Level 2
Financial assets
Money market funds		13,085
Available-for-sale investment securities	1,287,459	1,089,755
Stock in Federal Home Loan Bank	11,706	11,218
Loans receivable, net	5,261	13,333
Mortgage-servicing rights	0	0
Bank-owned life insurance	146,122	143,197
Derivative assets	798	453
Financial liabilities
Deposit liabilities	5,721,882	5,546,644
Short-term borrowings—other than bank	49,789	0
Other bank borrowings	188,513	193,991
Long-term debt, net	1,740,479	1,704,717
Derivative liabilities-window forward contracts	246	823
Estimated fair value | Level 2 | Hawaiian Electric Company, Inc. and Subsidiaries
Financial assets
Derivative assets	615
Financial liabilities
Short-term borrowings	43,990
Long-term debt, net	1,434,528	1,399,490
Derivative liabilities-window forward contracts	230	743
Estimated fair value | Level 3
Financial assets
Money market funds		0
Available-for-sale investment securities	15,427	15,427
Stock in Federal Home Loan Bank	0	0
Loans receivable, net	4,836,804	4,839,493
Mortgage-servicing rights	12,270	13,216
Bank-owned life insurance	0	0
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-window forward contracts	0	0
Estimated fair value | Level 3 | Hawaiian Electric Company, Inc. and Subsidiaries
Financial assets
Derivative assets	0
Financial liabilities
Short-term borrowings	0
Long-term debt, net	0	0
Derivative liabilities-window forward contracts	$ 0	$ 0