Bank segment - Mortgage servicing rights (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Valuation Allowance [Roll Forward]
Weighted average discount rate			2.826%
American Savings Bank (ASB)
Servicing Asset at Amortized Cost [Line Items]
Repurchase reserve						$ 100		$ 100
Mortgage service fees	$ 800	$ 700	$ 2,300	$ 2,100
Movement in Mortgage Loans on Real Estate [Roll Forward]
Servicing asset - beginning balance			9,373
Servicing asset - ending balance	9,070		9,070		$ 9,373
American Savings Bank (ASB) | Mortgage Servicing Rights (MSR)
Servicing Asset at Amortized Cost [Line Items]
Gross carrying amount						18,463	$ 17,271
Accumulated amortization						(9,393)	(7,898)
Valuation allowance	0	0	0	0	0	0	0	0
Net carrying amount						9,070	9,373	$ 9,191
Movement in Mortgage Loans on Real Estate [Roll Forward]
Servicing asset - beginning balance	9,181	9,016	9,373	8,884	8,884
Amount capitalized	394	824	1,192	1,944
Amortization	(505)	(649)	(1,495)	(1,637)
Other-than-temporary impairment	0	0	0	0
Servicing asset - ending balance	9,070	9,191	9,070	9,191	9,373
Valuation Allowance [Roll Forward]
Valuation allowance, beginning balance	0	0	0	0	0
Provision (recovery)	0	0	0	0
Other-than-temporary impairment	0	0	0	0
Valuation allowance, ending balance	0	0	$ 0	0	$ 0
Unpaid principal balance						1,212,730	1,188,380
Weighted average note-rate			3.94%		3.96%
Weighted average discount rate			10.00%		9.40%
Weighted average prepayment speed			9.20%		8.50%
Prepayment rate - 25 points adverse rate change						(878)	(567)
Prepayment rate - 50 points adverse rate change						(1,847)	(1,154)
Discount rate - 25 points adverse rate change						(111)	(128)
Discount rate - 50 points adverse rate change						$ (220)	$ (254)
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	39,800	70,000	$ 119,700	168,500
Gain on sale of mortgage loans	$ 500	$ 2,400	$ 1,900	$ 5,100