Bank segment - Reconciliation of Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Condensed Income Statements, Captions [Line Items]
Gain on sale of investment securities, net	$ 0	$ 653	$ 9,275	$ 653
Total revenues	641,427	770,882	1,927,558	2,147,982
Retirement defined benefits gain (expense)--other than service costs	(1,102)	(648)	(2,970)	(2,172)
Total expenses	541,866	674,227	1,696,739	1,900,756
Operating income	99,561	96,655	230,819	247,226
Income before income taxes	79,521	78,693	179,447	189,426
American Savings Bank (ASB)
Condensed Income Statements, Captions [Line Items]
Interest and dividend income	59,640	66,859	184,444	201,502
Total noninterest income	19,004	16,342	57,927	46,438
Gain on sale of investment securities, net	0	(653)	(9,275)	(653)
Total revenues	78,644	82,548	233,096	247,287
Total interest expense	2,348	4,806	9,394	14,284
Provision for credit losses	13,970	3,315	39,504	17,873
Noninterest expense	47,299	45,923	142,143	139,172
Retirement defined benefits gain (expense)--other than service costs	473	(196)	1,341	(276)
Total expenses	63,144	54,240	189,700	171,605
Operating income	15,500	28,308	43,396	75,682
Income before income taxes	$ 15,027	$ 29,157	$ 51,330	$ 76,611