Bank segment - Reconciliation of Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Condensed Income Statements, Captions [Line Items]
Total revenues	$ 771,535	$ 768,048	$ 2,148,635	$ 2,099,199
Less: Retirement defined benefits gain (expense)—other than service costs	(648)	(1,276)	(2,172)	(4,673)
Total expenses	674,227	669,984	1,900,756	1,850,447
Operating income	97,308	98,064	247,879	248,752
Income before income taxes	78,693	77,233	189,426	190,091
American Savings Bank (ASB)
Condensed Income Statements, Captions [Line Items]
Interest and dividend income	66,859	65,185	201,502	190,448
Total noninterest income	16,342	15,311	46,438	42,571
Total revenues	83,201	80,496	247,940	233,019
Total interest expense	4,806	4,039	14,284	11,169
Provision for loan losses	3,315	6,033	17,873	12,337
Noninterest expense	45,923	43,593	139,172	131,668
Less: Retirement defined benefits gain (expense)—other than service costs	(196)	433	(276)	1,223
Total expenses	54,240	53,232	171,605	153,951
Operating income	28,961	27,264	76,335	79,068
Income before income taxes	$ 29,157	$ 26,831	$ 76,611	$ 77,845