Bank segment - Mortgage servicing rights (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Valuation Allowance [Roll Forward]
Weighted average discount rate	3.262%
American Savings Bank (ASB)
Servicing Asset at Amortized Cost [Line Items]
Repurchase reserve				$ 100		$ 100
Mortgage service fees	$ 700	$ 800
Movement in Mortgage Loans on Real Estate [Roll Forward]
Servicing asset - beginning balance	8,639
Servicing asset - ending balance	8,541		$ 8,639
American Savings Bank (ASB) | Mortgage Servicing Rights (MSR)
Servicing Asset at Amortized Cost [Line Items]
Gross carrying amount				17,846	$ 17,511
Accumulated amortization				(9,305)	(8,872)
Valuation allowance	0	0	0	0	0	0
Net carrying amount				8,541	8,639	$ 9,294
Movement in Mortgage Loans on Real Estate [Roll Forward]
Servicing asset - beginning balance	8,639	9,373	9,373
Amount capitalized	335	436
Amortization	(433)	(515)
Other-than-temporary impairment	0	0
Servicing asset - ending balance	8,541	9,294	8,639
Valuation Allowance [Roll Forward]
Valuation allowance, beginning balance	0	0	0
Provision (recovery)	0	0
Other-than-temporary impairment	0	0
Valuation allowance, ending balance	$ 0	0	$ 0
Unpaid principal balance				1,184,160	1,195,454
Weighted average note-rate	3.94%		3.94%
Weighted average discount rate	10.00%		10.00%
Weighted average prepayment speed	7.10%		9.00%
Prepayment rate:
25 basis points adverse rate change				(378)	(869)
50 basis points adverse rate change				(883)	(1,828)
Discount rate:
25 basis points adverse rate change				(127)	(111)
50 basis points adverse rate change				$ (252)	$ (220)
American Savings Bank (ASB) | Measurement Band A
Valuation Allowance [Roll Forward]
Measurement band percent for risk categorization	0.50%
American Savings Bank (ASB) | Measurement Band B
Valuation Allowance [Roll Forward]
Measurement band percent for risk categorization	1.00%
American Savings Bank (ASB) | Residential loan
Servicing Asset at Amortized Cost [Line Items]
Proceeds from sale of mortgage loans	$ 33,100	40,600
Gain on sale of mortgage loans	$ 600	$ 800