Bank segment - Balance Sheets Data (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Assets
Cash and cash equivalents	$ 550,408		$ 679,546	$ 314,284
Investment securities
Available-for-sale investment securities, at fair value	1,061,687		1,136,439
Held-to-maturity, at amortized cost (fair value of $1,058,691 and $1,103,668, at June 30, 2024 and December 31, 2023, respectively)	1,179,182		1,201,314
Held-to-maturity investment securities	1,058,691
Stock in Federal Home Loan Bank, at cost	29,204		14,728
Allowance for credit losses	(66,813)	$ (71,057)	(74,372)	(69,068)	$ (71,296)	$ (72,216)
Loans held for investment, net	5,963,345		6,106,438
Loans held for sale, at lower of cost or fair value	13,904		15,168
Other	1,057,165		877,959
Goodwill	0		82,190
Total assets	17,055,414		17,243,821
Liabilities and shareholder’s equity
Other	749,621		778,349
Total liabilities	15,935,848		14,864,687
Retained earnings (deficit)	(326,642)		926,720
Accumulated other comprehensive loss, net of tax benefits
Accumulated other comprehensive loss, net of tax benefits	(297,557)		(289,350)
Common stock equity	1,085,273	$ 2,377,380	2,344,841	$ 2,249,377	$ 2,237,955	$ 2,202,499
Total liabilities and shareholders’ equity	17,055,414		17,243,821
Other assets
Premises and equipment, net	6,298,721		6,150,126
Total other assets	1,057,165		877,959
Other liabilities
Total other liabilities	749,621		778,349
American Savings Bank (ASB)
Assets
Cash and due from banks	139,114		184,383
Interest-bearing deposits	195,721		251,072
Cash and cash equivalents	334,835		435,455
Investment securities
Available-for-sale investment securities, at fair value	1,061,687		1,136,439
Held-to-maturity, at amortized cost (fair value of $1,058,691 and $1,103,668, at June 30, 2024 and December 31, 2023, respectively)	1,179,182		1,201,314
Held-to-maturity investment securities	1,058,691		1,103,668
Stock in Federal Home Loan Bank, at cost	29,204		14,728
Loans held for investment	6,030,158		6,180,810
Allowance for credit losses	(66,813)		(74,372)
Loans held for investment, net	5,963,345		6,106,438
Loans held for sale, at lower of cost or fair value	13,904		15,168
Other	698,648		681,460
Goodwill	0		82,190
Total assets	9,280,805		9,673,192
Liabilities and shareholder’s equity
Deposit liabilities—noninterest-bearing	2,515,062		2,599,762
Deposit liabilities—interest-bearing	5,521,411		5,546,016
Other borrowings	520,000		750,000
Other	226,488		247,563
Total liabilities	8,782,961		9,143,341
Common stock	1		1
Additional paid-in capital	359,048		358,067
Retained earnings (deficit)	439,202		464,055
Accumulated other comprehensive loss, net of tax benefits
Net unrealized losses on securities	(291,864)		(282,963)
Retirement benefit plans	(8,543)		(9,309)
Accumulated other comprehensive loss, net of tax benefits	(300,407)		(292,272)
Common stock equity	497,844		529,851
Total liabilities and shareholders’ equity	9,280,805		9,673,192
Other assets
Bank-owned life insurance	197,714		187,857
Premises and equipment, net	181,855		187,042
Accrued interest receivable	29,003		28,472
Mortgage-servicing rights	7,906		8,169
Low-income housing investments	104,394		112,234
Deferred tax asset	122,927		104,292
Other	54,849		53,394
Total other assets	698,648		681,460
Other liabilities
Accrued expenses	110,173		115,231
Cashier’s checks	37,372		40,479
Advance payments by borrowers	11,477		10,107
Other	67,466		81,746
Total other liabilities	$ 226,488		$ 247,563