Bank segment - Reconciliation of Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Condensed Income Statements, Captions [Line Items]
Gain on sale of investment securities, net	$ 9,275	$ 0	$ 9,275	$ 0
Total revenues	608,945	715,485	1,286,131	1,377,100
Total revenues	608,945	715,485	1,286,131	1,377,100
Retirement defined benefits gain (expense)--other than service costs	(934)	(761)	(1,868)	(1,524)
Total expenses	537,389	642,851	1,154,873	1,226,529
Operating income	71,556	72,634	131,258	150,571
Income before income taxes	60,230	52,694	99,926	110,733
American Savings Bank (ASB)
Condensed Income Statements, Captions [Line Items]
Interest and dividend income	59,829	66,155	124,804	134,643
Total noninterest income	24,160	15,532	38,923	30,096
Gain on sale of investment securities, net	(9,275)	0	(9,275)	0
Total revenues	74,714	81,687	154,452	164,739
Total interest expense	3,146	4,698	7,046	9,478
Provision for credit losses	15,133	7,688	25,534	14,558
Noninterest expense	48,376	48,009	94,844	93,249
Retirement defined benefits gain (expense)--other than service costs	434	(40)	868	(80)
Total expenses	66,221	60,435	126,556	117,365
Operating income	8,493	21,252	27,896	47,374
Income before income taxes	$ 17,334	$ 21,292	$ 36,303	$ 47,454