Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Jan. 01, 2014	Dec. 31, 2013
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total expenses	$ 620,081	$ 775,060	$ 1,739,619	$ 2,185,069
Operating income	97,095	92,036	239,331	264,433
Income taxes	29,516	27,264	70,406	76,302
Net income for common stock	50,673	47,808	117,557	134,876
Other	453,099		453,099		$ 542,523
Liabilities and Equity	11,573,466		11,573,466		11,185,142
Liabilities	9,618,172		9,618,172		9,360,276
Retained earnings	315,759		315,759		296,654
Common stock equity	1,921,001	1,800,457	1,921,001	1,800,457	1,790,573		$ 1,726,406
Net income	51,144	48,279	118,974	136,293
Increase in deferred income taxes			2,723	50,296
Change in other assets and liabilities			(38,033)	(56,326)
American Savings Bank (ASB)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of new accounting principle in period						$ 700
Low income housing tax credits, amortization	1,300		3,800
Low income housing tax credits, tax credits	1,300		3,900
Low income housing tax credits, other tax benefits	600		1,600
Income taxes	7,351	7,253	21,382	21,806
Other	307,089		307,089		305,416
Liabilities and Equity	5,855,497		5,855,497		5,566,222
Liabilities	5,298,100		5,298,100		5,032,434
Retained earnings	229,211		229,211		211,934
Common stock equity	557,397		557,397		533,788
Net income	13,451	13,253	39,777	39,188
Bank
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total expenses	48,289	43,030	138,063	126,778
Operating income	20,802	20,506	61,159	60,993
Income taxes	7,351	7,253	21,382	21,806
Net income for common stock	13,451	13,253	39,777	39,188
Net income	$ 13,451	13,253	$ 39,777	39,188
Scenario, Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in deferred income taxes				49,270
Change in other assets and liabilities				(47,760)
Scenario, Previously Reported | American Savings Bank (ASB)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income taxes		6,312		18,769
Net income for common stock		13,260		39,475
Other					304,435
Liabilities and Equity					5,565,241
Deferred Income Tax Liabilities And Other Liabilities					116,527
Liabilities					5,030,598
Retained earnings					212,789
Common stock equity					534,643
Scenario, Previously Reported | Bank | American Savings Bank (ASB)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total expenses		39,664		117,924
Operating income		19,572		58,244
Restatement Adjustment | Capital Expenditure Accruals
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in deferred income taxes				1,026
Change in other assets and liabilities				(8,566)
Accounting Standards Update 2014-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income taxes		27,264		76,302
Net income for common stock		47,808		134,876
Other					542,523
Liabilities and Equity					11,185,142
Deferred Income Tax Liabilities And Other Liabilities					633,570
Liabilities					9,360,276
Retained earnings					296,654		255,030
Common stock equity					1,790,573		1,726,406
Net income				136,293
Increase in deferred income taxes				50,296
Change in other assets and liabilities				(56,326)
Accounting Standards Update 2014-01 | American Savings Bank (ASB)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income taxes		7,253		21,806
Net income for common stock		13,253		39,188
Other					305,416
Liabilities and Equity					5,566,222
Deferred Income Tax Liabilities And Other Liabilities					118,363
Liabilities					5,032,434
Retained earnings					211,934
Common stock equity					533,788
Accounting Standards Update 2014-01 | Bank
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total expenses		43,030		126,778
Operating income		20,506		60,993
Accounting Standards Update 2014-01 | Bank | American Savings Bank (ASB)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total expenses		38,730		115,174
Operating income		20,506		60,994
Accounting Standards Update 2014-01 | Scenario, Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income taxes		26,323		73,265
Net income for common stock		47,815		135,163
Other					541,542
Liabilities and Equity					11,184,161
Deferred Income Tax Liabilities And Other Liabilities					631,734
Liabilities					9,358,440
Retained earnings					297,509		255,694
Common stock equity					1,791,428		1,727,070
Net income				136,580
Increase in deferred income taxes				48,900
Change in other assets and liabilities				(47,677)
Accounting Standards Update 2014-01 | Scenario, Previously Reported | Bank
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total expenses		43,964		129,528
Operating income		19,572		58,243
Accounting Standards Update 2014-01 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income taxes		941		3,037
Net income for common stock		(7)		(287)
Other					981
Liabilities and Equity					981
Deferred Income Tax Liabilities And Other Liabilities					1,836
Liabilities					1,836
Retained earnings					(855)		(664)
Common stock equity					(855)		$ (664)
Net income				(287)
Increase in deferred income taxes				370
Change in other assets and liabilities				(83)
Accounting Standards Update 2014-01 | Restatement Adjustment | American Savings Bank (ASB)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income taxes		941		3,037
Net income for common stock		(7)		(287)
Other					981
Liabilities and Equity					981
Deferred Income Tax Liabilities And Other Liabilities					1,836
Liabilities					1,836
Retained earnings					(855)
Common stock equity					$ (855)
Accounting Standards Update 2014-01 | Restatement Adjustment | Bank
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total expenses		(934)		(2,750)
Operating income		934		2,750
Accounting Standards Update 2014-01 | Restatement Adjustment | Bank | American Savings Bank (ASB)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total expenses		(934)		(2,750)
Operating income		$ 934		$ 2,750