Bank subsidiary (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net income	$ 48,707	$ 48,177	$ 123,920	$ 126,239
Net unrealized gains (losses) on securities:
Net unrealized gains (losses) on securities arising during the period, net of (taxes) benefits, of $1,049 and ($689) for the three months ended September 30, 2013 and 2012 and $7,081 and ($1,261) for the nine months ended September 30, 2013 and 2012, respectively	(1,589)	1,043	(10,724)	1,910
Net unrealized gains (losses) on securities arising during the period, (taxes) benefits	1,049	(689)	7,081	(1,261)
Less: reclassification adjustment for net realized gains, included in net income, net of taxes, of nil for the three months ended September 30, 2013 and 2012 and $488 and $53 for the nine months ended September 30, 2013 and 2012, respectively	0	0	(738)	(81)
Less: reclassification adjustment for net realized gains included in net income, taxes	0	0	488	53
Retirement benefit plans:
Amortization of transition obligation, prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits	5,789	3,826	17,490	11,467
Less: amortization of net loss, prior service gain and transition obligation included in net periodic benefit cost, tax benefits	3,697	2,443	11,173	7,321
Other comprehensive income (loss), net of taxes	(897)	1,586	(9,263)	3,447
Comprehensive income	47,339	49,292	113,240	128,269
American Savings Bank (ASB)
Net income	15,276	14,208	45,350	44,274
Net unrealized gains (losses) on securities:
Net unrealized gains (losses) on securities arising during the period, net of (taxes) benefits, of $1,049 and ($689) for the three months ended September 30, 2013 and 2012 and $7,081 and ($1,261) for the nine months ended September 30, 2013 and 2012, respectively	(1,589)	1,043	(10,724)	1,910
Net unrealized gains (losses) on securities arising during the period, (taxes) benefits	1,049	(689)	7,081	(1,261)
Less: reclassification adjustment for net realized gains, included in net income, net of taxes, of nil for the three months ended September 30, 2013 and 2012 and $488 and $53 for the nine months ended September 30, 2013 and 2012, respectively	0	0	(738)	(81)
Less: reclassification adjustment for net realized gains included in net income, taxes	0	0	488	53
Retirement benefit plans:
Amortization of transition obligation, prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits	420	266	3,043	769
Less: amortization of net loss, prior service gain and transition obligation included in net periodic benefit cost, tax benefits	278	176	2,010	508
Other comprehensive income (loss), net of taxes	(1,169)	1,309	(8,419)	2,598
Comprehensive income	$ 14,107	$ 15,517	$ 36,931	$ 46,872