Bank segment - Reconciliation of Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Income Statements, Captions [Line Items]
Total revenues	$ 645,874	$ 591,562
Less: Retirement defined benefits expense—other than service costs	1,833	1,876
Total expenses	573,985	521,824
Operating income	71,889	69,738
Income before income taxes	53,276	51,582
American Savings Bank (ASB)
Condensed Income Statements, Captions [Line Items]
Interest and dividend income	62,002	57,722
Noninterest income	13,417	15,134
Total revenues	75,419	72,856
Interest Expense	3,453	2,919
Provision for loan losses	3,541	3,907
Noninterest expense	43,925	41,870
Less: Retirement defined benefits expense—other than service costs	(387)	(195)
Total expenses	50,532	48,501
Operating income	24,887	24,355
Income before income taxes	$ 24,500	$ 24,160