Bank segment - Comprehensive income data (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015		Jun. 30, 2014
Condensed Statement of Income Captions [Line Items]
Net income	$ 35,491	$ 41,754	$ 67,830	[1]	$ 88,014	[1]
Net unrealized gains (losses) on securities:
Net unrealized gains (losses) on available-for-sale investment securities arising during the period, net of (taxes) benefits of $2,439, $(1,679), $161 and $(3,343) for the respective periods	(3,694)	2,543	(243)		5,063
Less: reclassification adjustment for net realized gains included in net income, net of taxes of nil, nil, nil and $1,132 for the respective periods	0	0	0		(1,715)
Retirement benefit plans:
Less: amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $255, $142, $514 and $286 for the respective periods	5,780	2,873	11,239		5,686
Other comprehensive income (loss), net of taxes	(3,127)	2,900	931		4,067
Comprehensive income	31,891	44,181	67,815		91,135
Net unrealized gains (losses) on securities arising during the period, taxes	2,439	(1,679)	161		(3,343)
Less: reclassification adjustment for net realized gains included in net income, taxes	0	0	0		(1,132)
Less: amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits	(3,691)	(1,836)	(7,177)		(3,632)
American Savings Bank (ASB)
Condensed Statement of Income Captions [Line Items]
Net income	12,851	11,536	26,326		25,935
Net unrealized gains (losses) on securities:
Net unrealized gains (losses) on available-for-sale investment securities arising during the period, net of (taxes) benefits of $2,439, $(1,679), $161 and $(3,343) for the respective periods	(3,694)	2,543	(243)		5,063
Less: reclassification adjustment for net realized gains included in net income, net of taxes of nil, nil, nil and $1,132 for the respective periods	0	0	0		(1,715)
Retirement benefit plans:
Less: amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $255, $142, $514 and $286 for the respective periods	387	215	779		434
Other comprehensive income (loss), net of taxes	(3,307)	2,758	536		3,782
Comprehensive income	9,544	14,294	26,862		29,717
Net unrealized gains (losses) on securities arising during the period, taxes	(2,439)	1,679	(161)		3,343
Less: reclassification adjustment for net realized gains included in net income, taxes	0	0	0		1,132
Less: amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits	$ (255)	$ (142)	$ (514)		$ (286)

[1] As restated - See Note 1, “Basis of presentation - Restatement of previously issued financial statements.”