Bank segment - Components of Investment Securities (Details) $ in Thousands	Sep. 30, 2024 USD ($) issue	Dec. 31, 2023 USD ($) issue
Available-for-sale
Amortized cost	$ 1,260,132
Available-for-sale investment securities, at fair value	1,084,083	$ 1,136,439
Held-to-maturity
Held-to-maturity investment securities, at amortized cost	1,159,229	1,201,314
Held-to-maturity investment securities	1,086,205
American Savings Bank (ASB)
Available-for-sale
Amortized cost	1,260,132	1,341,886
Gross unrealized gains	31	0
Gross unrealized losses	(176,080)	(205,447)
Available-for-sale investment securities, at fair value	$ 1,084,083	$ 1,136,439
Gross unrealized losses, less than 12 months, number of issues | issue	0	3
Gross unrealized losses, less than 12 months, fair value	$ 0	$ 1,649
Gross unrealized losses, less than 12 months, amount	$ 0	$ (22)
Gross unrealized losses, 12 months or longer, number of issues | issue	117	128
Gross unrealized losses, 12 months or longer, fair value	$ 1,067,418	$ 1,120,432
Gross unrealized losses, 12 months or more, amount	(176,080)	(205,425)
Held-to-maturity
Held-to-maturity investment securities, at amortized cost	1,159,229	1,201,314
Gross unrealized gains	6,355	2,221
Gross unrealized losses	(79,379)	(99,867)
Held-to-maturity investment securities	$ 1,086,205	$ 1,103,668
Less than 12 months, number of issues | issue	0	37
Less than 12 months, fair value	$ 0	$ 378,326
Less than 12 months, amount	$ 0	$ (7,610)
12 months or longer, number of issues | issue	68	46
12 months or longer: fair value	$ 702,883	$ 484,864
12 months or longer, amount	(79,379)	(92,257)
U.S. Treasury and federal agency obligations | American Savings Bank (ASB)
Available-for-sale
Amortized cost	7,789	12,437
Gross unrealized gains	0	0
Gross unrealized losses	(192)	(427)
Available-for-sale investment securities, at fair value	$ 7,597	$ 12,010
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	6	9
Gross unrealized losses, 12 months or longer, fair value	$ 7,597	$ 12,010
Gross unrealized losses, 12 months or more, amount	(192)	(427)
Held-to-maturity
Held-to-maturity investment securities, at amortized cost	59,935	59,917
Gross unrealized gains	0	0
Gross unrealized losses	(5,686)	(7,135)
Held-to-maturity investment securities	$ 54,249	$ 52,782
Less than 12 months, number of issues | issue	0	0
Less than 12 months, fair value	$ 0	$ 0
Less than 12 months, amount	$ 0	$ 0
12 months or longer, number of issues | issue	3	3
12 months or longer: fair value	$ 54,249	$ 52,782
12 months or longer, amount	(5,686)	(7,135)
Mortgage-backed securities | American Savings Bank (ASB)
Available-for-sale
Amortized cost	1,203,271	1,279,852
Gross unrealized gains	31	0
Gross unrealized losses	(174,675)	(202,684)
Available-for-sale investment securities, at fair value	$ 1,028,627	$ 1,077,168
Gross unrealized losses, less than 12 months, number of issues | issue	0	3
Gross unrealized losses, less than 12 months, fair value	$ 0	$ 1,649
Gross unrealized losses, less than 12 months, amount	$ 0	$ (22)
Gross unrealized losses, 12 months or longer, number of issues | issue	108	116
Gross unrealized losses, 12 months or longer, fair value	$ 1,025,897	$ 1,075,519
Gross unrealized losses, 12 months or more, amount	(174,675)	(202,662)
Held-to-maturity
Held-to-maturity investment securities, at amortized cost	1,099,294	1,141,397
Gross unrealized gains	6,355	2,221
Gross unrealized losses	(73,693)	(92,732)
Held-to-maturity investment securities	$ 1,031,956	$ 1,050,886
Less than 12 months, number of issues | issue	0	37
Less than 12 months, fair value	$ 0	$ 378,326
Less than 12 months, amount	$ 0	$ (7,610)
12 months or longer, number of issues | issue	65	43
12 months or longer: fair value	$ 648,634	$ 432,082
12 months or longer, amount	(73,693)	(85,122)
Corporate bonds | American Savings Bank (ASB)
Available-for-sale
Amortized cost	35,137	35,239
Gross unrealized gains	0	0
Gross unrealized losses	(1,213)	(2,336)
Available-for-sale investment securities, at fair value	$ 33,924	$ 32,903
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	3	3
Gross unrealized losses, 12 months or longer, fair value	$ 33,924	$ 32,903
Gross unrealized losses, 12 months or more, amount	(1,213)	(2,336)
Mortgage revenue bonds | American Savings Bank (ASB)
Available-for-sale
Amortized cost	13,935	14,358
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Available-for-sale investment securities, at fair value	$ 13,935	$ 14,358
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