Bank segment - Components of investment securities (Details) $ in Thousands	Sep. 30, 2021 USD ($) issue	Dec. 31, 2020 USD ($) issue
Available-for-sale
Available-for-sale investment securities, at fair value	$ 2,580,830	$ 1,970,417
Held-to-maturity
Amortized cost	491,871	226,947
Held-to-maturity investment securities	484,654
American Savings Bank (ASB)
Available-for-sale
Amortized cost	2,608,592	1,943,114
Gross unrealized gains	13,488	30,454
Gross unrealized losses	(41,250)	(3,151)
Available-for-sale investment securities, at fair value	$ 2,580,830	$ 1,970,417
Gross unrealized losses, Less than 12 months, Number of issues \| issue	106	22
Gross unrealized losses, Less than 12 months, Fair value	$ 1,792,604	$ 373,924
Gross unrealized losses, Less than 12 months, Amount	$ (36,651)	$ (3,151)
Gross unrealized losses, 12 months or longer, Number of issues \| issue	9	0
Gross unrealized losses, 12 months or longer, Fair value	$ 123,882	$ 0
Gross unrealized losses, 12 months or more, amount	(4,599)	0
Held-to-maturity
Amortized cost	491,871	226,947
Gross unrealized gains	2,487	3,846
Gross unrealized losses	(9,704)	(830)
Held-to-maturity investment securities	$ 484,654	$ 229,963
Less than 12 months: Number of issues \| issue	24	7
Less than 12 Months: Fair value	$ 345,848	$ 114,152
Less than 12 Months: Amount	$ (8,291)	$ (830)
12 months or longer: Number of issues \| issue	2	0
12 months or longer: Fair value	$ 23,860	$ 0
12 months or longer: Amount	(1,413)	0
U.S. Treasury and federal agency obligations \| American Savings Bank (ASB)
Available-for-sale
Amortized cost	90,831	60,260
Gross unrealized gains	1,334	2,062
Gross unrealized losses	(90)	0
Available-for-sale investment securities, at fair value	$ 92,075	$ 62,322
Gross unrealized losses, Less than 12 months, Number of issues \| issue	1	0
Gross unrealized losses, Less than 12 months, Fair value	$ 19,851	$ 0
Gross unrealized losses, Less than 12 months, Amount	$ (90)	$ 0
Gross unrealized losses, 12 months or longer, Number of issues \| issue	0	0
Gross unrealized losses, 12 months or longer, Fair value	$ 0	$ 0
Gross unrealized losses, 12 months or more, amount	0	0
Held-to-maturity
Amortized cost	40,064
Gross unrealized gains	100
Gross unrealized losses	(13)
Held-to-maturity investment securities	$ 40,151
Less than 12 months: Number of issues \| issue	1
Less than 12 Months: Fair value	$ 19,941
Less than 12 Months: Amount	$ (13)
12 months or longer: Number of issues \| issue	0
12 months or longer: Fair value	$ 0
12 months or longer: Amount	0
Mortgage-backed securities \| American Savings Bank (ASB)
Available-for-sale
Amortized cost	2,471,650	1,825,893
Gross unrealized gains	11,193	26,817
Gross unrealized losses	(41,160)	(3,151)
Available-for-sale investment securities, at fair value	$ 2,441,683	$ 1,849,559
Gross unrealized losses, Less than 12 months, Number of issues \| issue	105	22
Gross unrealized losses, Less than 12 months, Fair value	$ 1,772,753	$ 373,924
Gross unrealized losses, Less than 12 months, Amount	$ (36,561)	$ (3,151)
Gross unrealized losses, 12 months or longer, Number of issues \| issue	9	0
Gross unrealized losses, 12 months or longer, Fair value	$ 123,882	$ 0
Gross unrealized losses, 12 months or more, amount	(4,599)	0
Held-to-maturity
Amortized cost	451,807	226,947
Gross unrealized gains	2,387	3,846
Gross unrealized losses	(9,691)	(830)
Held-to-maturity investment securities	$ 444,503	$ 229,963
Less than 12 months: Number of issues \| issue	23	7
Less than 12 Months: Fair value	$ 325,907	$ 114,152
Less than 12 Months: Amount	$ (8,278)	$ (830)
12 months or longer: Number of issues \| issue	2	0
12 months or longer: Fair value	$ 23,860	$ 0
12 months or longer: Amount	(1,413)	0
Corporate bonds \| American Savings Bank (ASB)
Available-for-sale
Amortized cost	30,684	29,776
Gross unrealized gains	961	1,575
Gross unrealized losses	0	0
Available-for-sale investment securities, at fair value	$ 31,645	$ 31,351
Gross unrealized losses, Less than 12 months, Number of issues \| issue	0	0
Gross unrealized losses, Less than 12 months, Fair value	$ 0	$ 0
Gross unrealized losses, Less than 12 months, Amount	$ 0	$ 0
Gross unrealized losses, 12 months or longer, Number of issues \| issue	0	0
Gross unrealized losses, 12 months or longer, Fair value	$ 0	$ 0
Gross unrealized losses, 12 months or more, amount	0	0
Mortgage revenue bonds \| American Savings Bank (ASB)
Available-for-sale
Amortized cost	15,427	27,185
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Available-for-sale investment securities, at fair value	$ 15,427	$ 27,185
Gross unrealized losses, Less than 12 months, Number of issues \| issue	0	0
Gross unrealized losses, Less than 12 months, Fair value	$ 0	$ 0
Gross unrealized losses, Less than 12 months, Amount	$ 0	$ 0
Gross unrealized losses, 12 months or longer, Number of issues \| issue	0	0
Gross unrealized losses, 12 months or longer, Fair value	$ 0	$ 0
Gross unrealized losses, 12 months or more, amount	$ 0	$ 0

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Held-To-Maturity Securities, More Than 12 Months, Number Of Issues

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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