Bank segment - Mortgage servicing rights (Details) - American Savings Bank (ASB) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)
Servicing Asset at Amortized Cost [Line Items]
Repurchase reserve					$ 100		$ 100
Mortgage service fees	$ 700	$ 800	$ 2,200	$ 2,300
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Servicing asset - beginning balance			8,639
Servicing asset - ending balance	8,426		8,426
Residential loan
Servicing Asset at Amortized Cost [Line Items]
Proceeds from sale of mortgage loans	31,900	39,800	109,300	119,700
Gain on sale of mortgage loans	200	500	1,400	1,900
Servicing contracts
Servicing Asset at Amortized Cost [Line Items]
Gross carrying amount					18,543	$ 17,511
Accumulated amortization					(10,117)	(8,872)
Valuation allowance	0	0	0	0	0	0	0
Net carrying amount					8,426	8,639	$ 9,070
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Servicing asset - beginning balance	8,509	9,181	8,639	9,373
Amount capitalized	305	394	1,032	1,192
Amortization	(388)	(505)	(1,245)	(1,495)
Other-than-temporary impairment	0	0	0	0
Servicing asset - ending balance	8,426	9,070	8,426	9,070
Valuation Allowance [Roll Forward]
Valuation allowance, beginning balance	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
Unpaid principal balance					1,206,025	1,195,454
Prepayment rate:
25 basis points adverse rate change					(379)	(869)
50 basis points adverse rate change					(836)	(1,828)
Discount rate:
25 basis points adverse rate change					(134)	(111)
50 basis points adverse rate change					$ (265)	$ (220)
Servicing contracts | Note rate
Valuation Allowance [Roll Forward]
Weighted average measurement input					0.0398	0.0394
Servicing contracts | Discount rate
Valuation Allowance [Roll Forward]
Weighted average measurement input					0.100	0.100
Servicing contracts | Prepayment speed
Valuation Allowance [Roll Forward]
Weighted average measurement input					0.070	0.090
Measurement Band A
Valuation Allowance [Roll Forward]
Measurement band percent for risk categorization			0.50%
Measurement Band B
Valuation Allowance [Roll Forward]
Measurement band percent for risk categorization			1.00%