Bank segment - Components of Investment Securities (Details) $ in Thousands	Jun. 30, 2023 USD ($) issue	Dec. 31, 2022 USD ($) issue
Available-for-sale
Amortized cost	$ 1,608,897
Available-for-sale investment securities, at fair value	1,368,037	$ 1,429,667
Held-to-maturity
Held-to-maturity investment securities, at amortized cost	1,224,917	1,251,747
Held-to-maturity investment securities	1,121,995
American Savings Bank (ASB)
Available-for-sale
Amortized cost	1,608,897	1,678,205
Gross unrealized gains	0	0
Gross unrealized losses	(240,860)	(248,538)
Available-for-sale investment securities, at fair value	$ 1,368,037	$ 1,429,667
Gross unrealized losses, less than 12 months, number of issues | issue	8	129
Gross unrealized losses, less than 12 months, fair value	$ 36,332	$ 526,681
Gross unrealized losses, less than 12 months, amount	$ (3,863)	$ (61,147)
Gross unrealized losses, 12 months or longer, number of issues | issue	194	75
Gross unrealized losses, 12 months or longer, fair value	$ 1,317,075	$ 888,084
Gross unrealized losses, 12 months or more, amount	(236,997)	(187,391)
Held-to-maturity
Held-to-maturity investment securities, at amortized cost	1,224,917	1,251,747
Gross unrealized gains	2,449	2,670
Gross unrealized losses	(105,371)	(103,446)
Held-to-maturity investment securities	$ 1,121,995	$ 1,150,971
Less than 12 months, number of issues | issue	33	23
Less than 12 months, fair value	$ 322,971	$ 200,503
Less than 12 months, amount	$ (6,521)	$ (13,815)
12 months or longer, number of issues | issue	43	53
12 months or longer: fair value	$ 454,876	$ 601,792
12 months or longer, amount	(98,850)	(89,631)
U.S. Treasury and federal agency obligations | American Savings Bank (ASB)
Available-for-sale
Amortized cost	84,728	88,344
Gross unrealized gains	0	0
Gross unrealized losses	(6,981)	(7,281)
Available-for-sale investment securities, at fair value	$ 77,747	$ 81,063
Gross unrealized losses, less than 12 months, number of issues | issue	0	12
Gross unrealized losses, less than 12 months, fair value	$ 0	$ 41,201
Gross unrealized losses, less than 12 months, amount	$ 0	$ (2,120)
Gross unrealized losses, 12 months or longer, number of issues | issue	14	4
Gross unrealized losses, 12 months or longer, fair value	$ 77,747	$ 39,862
Gross unrealized losses, 12 months or more, amount	(6,981)	(5,161)
Held-to-maturity
Held-to-maturity investment securities, at amortized cost	59,906	59,894
Gross unrealized gains	0	0
Gross unrealized losses	(8,207)	(8,478)
Held-to-maturity investment securities	$ 51,699	$ 51,416
Less than 12 months, number of issues | issue	0	1
Less than 12 months, fair value	$ 0	$ 16,874
Less than 12 months, amount	$ 0	$ (3,222)
12 months or longer, number of issues | issue	3	2
12 months or longer: fair value	$ 51,699	$ 34,542
12 months or longer, amount	(8,207)	(5,256)
Mortgage-backed securities | American Savings Bank (ASB)
Available-for-sale
Amortized cost	1,465,232	1,530,582
Gross unrealized gains	0	0
Gross unrealized losses	(230,718)	(237,614)
Available-for-sale investment securities, at fair value	$ 1,234,514	$ 1,292,968
Gross unrealized losses, less than 12 months, number of issues | issue	8	113
Gross unrealized losses, less than 12 months, fair value	$ 36,332	$ 455,836
Gross unrealized losses, less than 12 months, amount	$ (3,863)	$ (56,999)
Gross unrealized losses, 12 months or longer, number of issues | issue	175	70
Gross unrealized losses, 12 months or longer, fair value	$ 1,198,182	$ 837,132
Gross unrealized losses, 12 months or more, amount	(226,855)	(180,615)
Held-to-maturity
Held-to-maturity investment securities, at amortized cost	1,165,011	1,191,853
Gross unrealized gains	2,449	2,670
Gross unrealized losses	(97,164)	(94,968)
Held-to-maturity investment securities	$ 1,070,296	$ 1,099,555
Less than 12 months, number of issues | issue	33	22
Less than 12 months, fair value	$ 322,971	$ 183,629
Less than 12 months, amount	$ (6,521)	$ (10,593)
12 months or longer, number of issues | issue	40	51
12 months or longer: fair value	$ 403,177	$ 567,250
12 months or longer, amount	(90,643)	(84,375)
Corporate bonds | American Savings Bank (ASB)
Available-for-sale
Amortized cost	44,307	44,377
Gross unrealized gains	0	0
Gross unrealized losses	(3,161)	(3,643)
Available-for-sale investment securities, at fair value	$ 41,146	$ 40,734
Gross unrealized losses, less than 12 months, number of issues | issue	0	4
Gross unrealized losses, less than 12 months, fair value	$ 0	$ 29,644
Gross unrealized losses, less than 12 months, amount	$ 0	$ (2,028)
Gross unrealized losses, 12 months or longer, number of issues | issue	5	1
Gross unrealized losses, 12 months or longer, fair value	$ 41,146	$ 11,090
Gross unrealized losses, 12 months or more, amount	(3,161)	(1,615)
Mortgage revenue bonds | American Savings Bank (ASB)
Available-for-sale
Amortized cost	14,630	14,902
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Available-for-sale investment securities, at fair value	$ 14,630	$ 14,902
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