Fair value measurements - Summary of financial assets and liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financial assets
Available-for-sale investment securities	$ 1,228,922	$ 1,105,182
Financial liabilities
Short-term borrowings—other than bank	2,300	0
Other bank borrowings	200,154	192,618
Carrying or notional amount
Financial assets
Money market funds	6	13,085
Available-for-sale investment securities	1,228,922	1,105,182
Stock in Federal Home Loan Bank	11,706	11,218
Loans receivable, net	4,679,728	4,701,977
Mortgage-servicing rights	9,294	9,373
Bank-owned life insurance	144,661	143,197
Derivative assets	22,986	23,578
Financial liabilities
Deposit liabilities	5,675,090	5,548,929
Short-term borrowings—other than bank	2,300	0
Other bank borrowings	200,154	192,618
Long-term debt, net	1,618,651	1,619,019
Derivative liabilities	36,743	53,852
Carrying or notional amount | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,318,871	1,319,260
Derivative liabilities	15,838	20,734
Short-term borrowings	1,500
Estimated fair value
Financial assets
Money market funds	6	13,085
Available-for-sale investment securities	1,228,922	1,105,182
Stock in Federal Home Loan Bank	11,706	11,218
Loans receivable, net	4,826,980	4,852,826
Mortgage-servicing rights	13,650	13,216
Bank-owned life insurance	144,661	143,197
Derivative assets	317	453
Financial liabilities
Deposit liabilities	5,671,729	5,546,644
Short-term borrowings—other than bank	2,300	0
Other bank borrowings	201,000	193,991
Long-term debt, net	1,707,954	1,704,717
Derivative liabilities	381	952
Estimated fair value | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,402,690	1,399,490
Derivative liabilities	277	743
Short-term borrowings	1,500
Estimated fair value | Level 1
Financial assets
Money market funds	0	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	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	98	129
Estimated fair value | Level 1 | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	0	0
Derivative liabilities	0	0
Short-term borrowings	0
Estimated fair value | Level 2
Financial assets
Money market funds	6	13,085
Available-for-sale investment securities	1,213,495	1,089,755
Stock in Federal Home Loan Bank	11,706	11,218
Loans receivable, net	10,881	13,333
Mortgage-servicing rights	0	0
Bank-owned life insurance	144,661	143,197
Derivative assets	317	453
Financial liabilities
Deposit liabilities	5,671,729	5,546,644
Short-term borrowings—other than bank	2,300	0
Other bank borrowings	201,000	193,991
Long-term debt, net	1,707,954	1,704,717
Derivative liabilities	283	823
Estimated fair value | Level 2 | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,402,690	1,399,490
Derivative liabilities	277	743
Short-term borrowings	1,500
Estimated fair value | Level 3
Financial assets
Money market funds	0	0
Available-for-sale investment securities	15,427	15,427
Stock in Federal Home Loan Bank	0	0
Loans receivable, net	4,816,099	4,839,493
Mortgage-servicing rights	13,650	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	0	0
Estimated fair value | Level 3 | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	0	0
Derivative liabilities	0	$ 0
Short-term borrowings	$ 0