Bank segment - Components of investment securities (Details) $ in Thousands	Mar. 31, 2023 USD ($) issue	Dec. 31, 2022 USD ($) issue
Available-for-sale
Amortized cost	$ 1,645,610
Available-for-sale investment securities, at fair value	1,419,755	$ 1,429,667
Held-to-maturity
Amortized cost	1,238,185	1,251,747
Held-to-maturity investment securities	1,158,090
American Savings Bank (ASB)
Available-for-sale
Amortized cost	1,645,610	1,678,205
Gross unrealized gains	1	0
Gross unrealized losses	(225,856)	(248,538)
Available-for-sale investment securities, at fair value	$ 1,419,755	$ 1,429,667
Gross unrealized losses, less than 12 months, number of issues | issue	26	129
Gross unrealized losses, less than 12 months, fair value	$ 98,678	$ 526,681
Gross unrealized losses, less than 12 months, amount	$ (7,417)	$ (61,147)
Gross unrealized losses, 12 months or longer, number of issues | issue	175	75
Gross unrealized losses, 12 months or longer, fair value	$ 1,305,736	$ 888,084
Gross unrealized losses, 12 months or more, amount	(218,439)	(187,391)
Held-to-maturity
Amortized cost	1,238,185	1,251,747
Gross unrealized gains	8,875	2,670
Gross unrealized losses	(88,970)	(103,446)
Held-to-maturity investment securities	$ 1,158,090	$ 1,150,971
Less than 12 months, number of issues | issue	6	23
Less than 12 months, fair value	$ 64,288	$ 200,503
Less than 12 months, amount	$ (532)	$ (13,815)
12 months or longer, number of issues | issue	44	53
12 months or longer: fair value	$ 480,248	$ 601,792
12 months or longer, amount	(88,438)	(89,631)
U.S. Treasury and federal agency obligations | American Savings Bank (ASB)
Available-for-sale
Amortized cost	85,786	88,344
Gross unrealized gains	0	0
Gross unrealized losses	(6,042)	(7,281)
Available-for-sale investment securities, at fair value	$ 79,744	$ 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	$ 79,744	$ 39,862
Gross unrealized losses, 12 months or more, amount	(6,042)	(5,161)
Held-to-maturity
Amortized cost	59,900	59,894
Gross unrealized gains	0	0
Gross unrealized losses	(7,172)	(8,478)
Held-to-maturity investment securities	$ 52,728	$ 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	$ 52,728	$ 34,542
12 months or longer, amount	(7,172)	(5,256)
Mortgage-backed securities | American Savings Bank (ASB)
Available-for-sale
Amortized cost	1,500,717	1,530,582
Gross unrealized gains	1	0
Gross unrealized losses	(216,783)	(237,614)
Available-for-sale investment securities, at fair value	$ 1,283,935	$ 1,292,968
Gross unrealized losses, less than 12 months, number of issues | issue	24	113
Gross unrealized losses, less than 12 months, fair value	$ 89,727	$ 455,836
Gross unrealized losses, less than 12 months, amount	$ (7,367)	$ (56,999)
Gross unrealized losses, 12 months or longer, number of issues | issue	158	70
Gross unrealized losses, 12 months or longer, fair value	$ 1,193,633	$ 837,132
Gross unrealized losses, 12 months or more, amount	(209,416)	(180,615)
Held-to-maturity
Amortized cost	1,178,285	1,191,853
Gross unrealized gains	8,875	2,670
Gross unrealized losses	(81,798)	(94,968)
Held-to-maturity investment securities	$ 1,105,362	$ 1,099,555
Less than 12 months, number of issues | issue	6	22
Less than 12 months, fair value	$ 64,288	$ 183,629
Less than 12 months, amount	$ (532)	$ (10,593)
12 months or longer, number of issues | issue	41	51
12 months or longer: fair value	$ 427,520	$ 567,250
12 months or longer, amount	(81,266)	(84,375)
Corporate bonds | American Savings Bank (ASB)
Available-for-sale
Amortized cost	44,341	44,377
Gross unrealized gains	0	0
Gross unrealized losses	(3,031)	(3,643)
Available-for-sale investment securities, at fair value	$ 41,310	$ 40,734
Gross unrealized losses, less than 12 months, number of issues | issue	2	4
Gross unrealized losses, less than 12 months, fair value	$ 8,951	$ 29,644
Gross unrealized losses, less than 12 months, amount	$ (50)	$ (2,028)
Gross unrealized losses, 12 months or longer, number of issues | issue	3	1
Gross unrealized losses, 12 months or longer, fair value	$ 32,359	$ 11,090
Gross unrealized losses, 12 months or more, amount	(2,981)	(1,615)
Mortgage revenue bonds | American Savings Bank (ASB)
Available-for-sale
Amortized cost	14,766	14,902
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Available-for-sale investment securities, at fair value	$ 14,766	$ 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