Bank segment (HEI only) - Available For Sale Investment Securities (Details) $ in Thousands	Dec. 31, 2020 USD ($) issues	Dec. 31, 2019 USD ($) issues
Available-for-sale
Total amortized cost	$ 1,943,114
Available-for-sale investment securities	1,970,417	$ 1,232,826
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Debt Securities, Held-to-maturity	226,947	139,451
Held-to-maturity investment securities	229,963	143,467
American Savings Bank (ASB)
Available-for-sale
Total amortized cost	1,943,114	1,229,438
Gross unrealized gains	30,454	8,015
Gross unrealized losses	(3,151)	(4,627)
Available-for-sale investment securities	$ 1,970,417	$ 1,232,826
Number of issues, less than 12 months | issues	22	21
Fair value, less than 12 months	$ 373,924	$ 156,181
Gross unrealized losses, less than 12 months	$ (3,151)	$ (830)
Number of issues, more than 12 months | issues	0	78
Fair value, 12 months or longer	$ 0	$ 345,657
Gross unrealized losses, 12 months or longer	0	(3,797)
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Debt Securities, Held-to-maturity	226,947	139,451
Gross unrealized gains	3,846	4,087
Gross unrealized losses	(830)	(71)
Held-to-maturity investment securities	$ 229,963	$ 143,467
Number of issues, less than 12 months | issues	7	1
Fair value, less than 12 months	$ 114,152	$ 12,986
Gross unrealized losses, less than 12 months	$ (830)	$ (71)
Number of issues, more than 12 months | issues	0	0
Fair value, 12 months or longer	$ 0	$ 0
Gross unrealized losses, 12 months or longer	0	0
American Savings Bank (ASB) | U.S. Treasury and federal agency obligations
Available-for-sale
Total amortized cost	60,260	117,255
Gross unrealized gains	2,062	652
Gross unrealized losses	0	(120)
Available-for-sale investment securities	$ 62,322	$ 117,787
Number of issues, less than 12 months | issues	0	2
Fair value, less than 12 months	$ 0	$ 4,110
Gross unrealized losses, less than 12 months	$ 0	$ (11)
Number of issues, more than 12 months | issues	0	3
Fair value, 12 months or longer	$ 0	$ 27,637
Gross unrealized losses, 12 months or longer	0	(109)
American Savings Bank (ASB) | Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies
Available-for-sale
Total amortized cost	1,825,893	1,024,892
Gross unrealized gains	26,817	6,000
Gross unrealized losses	(3,151)	(4,507)
Available-for-sale investment securities	$ 1,849,559	$ 1,026,385
Number of issues, less than 12 months | issues	22	19
Fair value, less than 12 months	$ 373,924	$ 152,071
Gross unrealized losses, less than 12 months	$ (3,151)	$ (819)
Number of issues, more than 12 months | issues	0	75
Fair value, 12 months or longer	$ 0	$ 318,020
Gross unrealized losses, 12 months or longer	0	(3,688)
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Debt Securities, Held-to-maturity	226,947	139,451
Gross unrealized gains	3,846	4,087
Gross unrealized losses	(830)	(71)
Held-to-maturity investment securities	$ 229,963	$ 143,467
Number of issues, less than 12 months | issues	7	1
Fair value, less than 12 months	$ 114,152	$ 12,986
Gross unrealized losses, less than 12 months	$ (830)	$ (71)
Number of issues, more than 12 months | issues	0	0
Fair value, 12 months or longer	$ 0	$ 0
Gross unrealized losses, 12 months or longer	0	0
American Savings Bank (ASB) | Corporate bonds
Available-for-sale
Total amortized cost	29,776	58,694
Gross unrealized gains	1,575	1,363
Gross unrealized losses	0	0
Available-for-sale investment securities	$ 31,351	$ 60,057
Number of issues, less than 12 months | issues	0	0
Fair value, less than 12 months	$ 0	$ 0
Gross unrealized losses, less than 12 months	$ 0	$ 0
Number of issues, more than 12 months | issues	0	0
Fair value, 12 months or longer	$ 0	$ 0
Gross unrealized losses, 12 months or longer	0	0
American Savings Bank (ASB) | Mortgage revenue bonds
Available-for-sale
Total amortized cost	27,185	28,597
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Available-for-sale investment securities	$ 27,185	$ 28,597
Number of issues, less than 12 months | issues	0	0
Fair value, less than 12 months	$ 0	$ 0
Gross unrealized losses, less than 12 months	$ 0	$ 0
Number of issues, more than 12 months | issues	0	0
Fair value, 12 months or longer	$ 0	$ 0
Gross unrealized losses, 12 months or longer	$ 0	$ 0