Bank segment - Reconciliation of Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Income Statements, Captions [Line Items]
Total revenues	$ 715,485	$ 685,277	$ 1,377,100	$ 1,331,151
Less: Retirement defined benefits gain (expense)—other than service costs	(761)	(1,564)	(1,524)	(3,397)
Total expenses	642,851	606,478	1,226,529	1,180,463
Operating income	72,634	78,799	150,571	150,688
Income before income taxes	52,694	59,582	110,733	112,858
American Savings Bank (ASB)
Condensed Income Statements, Captions [Line Items]
Interest and dividend income	66,155	63,261	134,643	125,263
Total noninterest income	15,532	13,843	30,096	27,260
Total revenues	81,687	77,104	164,739	152,523
Total interest expense	4,698	3,677	9,478	7,130
Provision for loan losses	7,688	2,763	14,558	6,304
Noninterest expense	48,009	44,150	93,249	88,075
Less: Retirement defined benefits gain (expense)—other than service costs	(40)	403	(80)	790
Total expenses	60,435	50,187	117,365	100,719
Operating income	21,252	26,917	47,374	51,804
Income before income taxes	$ 21,292	$ 26,514	$ 47,454	$ 51,014