Bank segment - Balance Sheets Data (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Assets
Cash and cash equivalents	$ 1,159,635			$ 679,546	$ 667,129
Investment securities
Available-for-sale investment securities, at fair value	1,084,083			1,136,439
Held-to-maturity, at amortized cost (fair value of $1,086,205 and $1,103,668, at September 30, 2024 and December 31, 2023, respectively)	1,159,229			1,201,314
Held-to-maturity investment securities	1,086,205
Stock in Federal Home Loan Bank, at cost	29,204			14,728
Allowance for credit losses	(64,796)	$ (66,813)		(74,372)	(76,366)	$ (69,068)		$ (72,216)
Loans held for investment, net	5,972,614			6,106,438
Loans held for sale, at lower of cost or fair value	2,704			15,168
Other	1,088,417			877,959
Goodwill	0			82,190
Total assets	17,731,228			17,243,821
Liabilities and shareholder’s equity
Other	736,459			778,349
Total liabilities	16,119,894			14,864,687
Retained earnings (deficit)	(431,044)			926,720
Accumulated other comprehensive loss, net of tax benefits
Accumulated other comprehensive loss, net of tax benefits	(258,197)			(289,350)
Common stock equity	1,577,041	$ 1,085,273	$ 2,377,380	2,344,841	$ 2,224,354	$ 2,249,377	$ 2,237,955	$ 2,202,499
Total liabilities and shareholders’ equity	17,731,228			17,243,821
Other assets
Premises and equipment, net	6,296,088			6,150,126
Total other assets	1,088,417			877,959
Other liabilities
Total other liabilities	736,459			778,349
American Savings Bank (ASB)
Assets
Cash and due from banks	155,869			184,383
Interest-bearing deposits	176,784			251,072
Cash and cash equivalents	332,653			435,455
Investment securities
Available-for-sale investment securities, at fair value	1,084,083			1,136,439
Held-to-maturity, at amortized cost (fair value of $1,086,205 and $1,103,668, at September 30, 2024 and December 31, 2023, respectively)	1,159,229			1,201,314
Held-to-maturity investment securities	1,086,205			1,103,668
Stock in Federal Home Loan Bank, at cost	29,204			14,728
Loans held for investment	6,037,410			6,180,810
Allowance for credit losses	(64,796)			(74,372)
Loans held for investment, net	5,972,614			6,106,438
Loans held for sale, at lower of cost or fair value	2,704			15,168
Other	687,359			681,460
Goodwill	0			82,190
Total assets	9,267,846			9,673,192
Liabilities and shareholder’s equity
Deposit liabilities—noninterest-bearing	2,486,717			2,599,762
Deposit liabilities—interest-bearing	5,512,493			5,546,016
Other borrowings	520,000			750,000
Other	191,512			247,563
Total liabilities	8,710,722			9,143,341
Common stock	1			1
Additional paid-in capital	359,346			358,067
Retained earnings (deficit)	457,980			464,055
Accumulated other comprehensive loss, net of tax benefits
Net unrealized losses on securities	(251,703)			(282,963)
Retirement benefit plans	(8,500)			(9,309)
Accumulated other comprehensive loss, net of tax benefits	(260,203)			(292,272)
Common stock equity	557,124			529,851
Total liabilities and shareholders’ equity	9,267,846			9,673,192
Other assets
Bank-owned life insurance	199,741			187,857
Premises and equipment, net	180,073			187,042
Accrued interest receivable	28,764			28,472
Mortgage-servicing rights	7,722			8,169
Low-income housing investments	100,499			112,234
Deferred tax asset	108,338			104,292
Other	62,222			53,394
Total other assets	687,359			681,460
Other liabilities
Accrued expenses	80,788			115,231
Cashier’s checks	35,625			40,479
Advance payments by borrowers	4,373			10,107
Other	70,726			81,746
Total other liabilities	$ 191,512			$ 247,563