Bank segment - Mortgage servicing rights (Details) - American Savings Bank (ASB) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)
Servicing Asset at Amortized Cost [Line Items]
Repurchase reserve					$ 100		$ 100
Mortgage service fees	$ 800	$ 700	$ 2,200	$ 2,200
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Servicing asset - beginning balance			8,062
Servicing asset - ending balance	8,567		8,567
Residential loan
Servicing Asset at Amortized Cost [Line Items]
Proceeds from sale of mortgage loans	87,800	31,900	177,300	109,300
Gain on sale of mortgage loans	1,500	200	3,100	1,400
Servicing contracts
Servicing Asset at Amortized Cost [Line Items]
Gross carrying amount					20,413	$ 18,556
Accumulated amortization					(11,846)	(10,494)
Valuation allowance	0	0	0	0	0	0	0
Net carrying amount					8,567	8,062	$ 8,426
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Servicing asset - beginning balance	8,103	8,509	8,062	8,639
Amount capitalized	995	305	1,857	1,032
Amortization	(531)	(388)	(1,352)	(1,245)
Other-than-temporary impairment	0	0	0	0
Servicing asset - ending balance	8,567	8,426	8,567	8,426
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					1,232,240	1,188,514
Prepayment rate:
25 basis points adverse rate change					(1,058)	(250)
50 basis points adverse rate change					(2,093)	(566)
Discount rate:
25 basis points adverse rate change					(90)	(139)
50 basis points adverse rate change					$ (180)	$ (275)
Servicing contracts | Note rate
Valuation Allowance [Roll Forward]
Weighted average measurement input					0.0399	0.0398
Servicing contracts | Discount rate
Valuation Allowance [Roll Forward]
Weighted average measurement input					0.093	0.100
Servicing contracts | Prepayment speed
Valuation Allowance [Roll Forward]
Weighted average measurement input					0.128	0.065