Bank segment - Balance sheet data (Details) - USD ($) $ in Thousands	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Assets
Available-for-sale investment securities, at fair value	$ 590,648	$ 550,394
Stock in Federal Home Loan Bank of Seattle, at cost	63,711	69,302
Loans receivable held for investment, net	4,401,504	4,389,033
Loans held for sale, at lower of cost or fair value	9,906	8,424
Other	481,531	542,523
Goodwill	82,190	82,190
Total assets	11,273,447	11,185,142
Liabilities
Other	456,338	531,230
Total liabilities	$ 9,341,245	$ 9,360,276
Commitments and contingencies
Equity [Abstract]
Retained earnings	$ 296,680	$ 296,654
Accumulated other comprehensive income (loss), net of taxes:
Accumulated other comprehensive loss, net of tax benefits	(23,320)	(27,378)	$ (15,583)	$ (16,750)
Total shareholders’ equity	1,897,909	1,790,573	$ 1,745,124	$ 1,726,406
Total liabilities and shareholders’ equity	11,273,447	11,185,142
Other assets
Property, plant and equipment, net of accumulated depreciation	4,190,835	4,148,774
Total Other Assets	481,531	542,523
Other liabilities
Total other liabilities	456,338	531,230
Balance Sheet related disclosures
Securities sold under agreements to repurchase	212,000	191,000
American Savings Bank (ASB)
Assets
Cash and due from banks	98,484	107,233
Interest-bearing deposits	172,517	54,230
Available-for-sale investment securities, at fair value	590,648	550,394
Stock in Federal Home Loan Bank of Seattle, at cost	63,711	69,302
Loans receivable held for investment	4,447,299	4,434,651
Allowance for loan losses	(45,795)	(45,618)
Loans receivable held for investment, net	4,401,504	4,389,033
Loans held for sale, at lower of cost or fair value	9,906	8,424
Other	305,917	305,416
Goodwill	82,190	82,190
Total assets	5,724,877	5,566,222
Liabilities
Deposit liabilities-noninterest-bearing	1,420,085	1,342,794
Deposit liabilities-interest-bearing	3,331,243	3,280,621
Other borrowings	312,094	290,656
Other	117,849	118,363
Total liabilities	$ 5,181,271	$ 5,032,434
Commitments and contingencies
Equity [Abstract]
Common stock	$ 1	$ 1
Additional paid in capital	338,411	338,411
Retained earnings	217,909	211,934
Accumulated other comprehensive income (loss), net of taxes:
Net unrealized losses on securities	3,913	462
Accumulated other comprehensive loss, net of tax benefits	(16,628)	(17,020)
Accumulated other comprehensive loss, net of tax benefits	(12,715)	(16,558)
Total shareholders’ equity	543,606	533,788
Other assets
Bank-owned life insurance	135,141	134,115
Property, plant and equipment, net of accumulated depreciation	85,174	92,407
Prepaid expenses	4,892	3,196
Accrued interest receivable	13,720	13,632
Mortgage-servicing rights	11,965	11,540
Low-income housing equity investments	32,140	33,438
Real estate acquired in settlement of loans, net	665	891
Other	22,220	16,197
Total Other Assets	305,917	305,416
Other liabilities
Accrued expenses	29,670	37,880
Federal and state income taxes payable	36,010	28,642
Cashier's checks	24,686	20,509
Advance payments by borrowers	5,904	9,652
Other	21,579	21,680
Total other liabilities	117,849	118,363
Balance Sheet related disclosures
Securities sold under agreements to repurchase	212,000	191,000
Advances from Federal Home Loan Bank	$ 100,000	$ 100,000