Bank segment - Mortgage servicing rights (Details) - American Savings Bank (ASB) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)
Servicing Asset at Amortized Cost [Line Items]
Repurchase reserve			$ 100		$ 100
Mortgage service fees	$ 800	$ 700
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Servicing asset - beginning balance	9,101
Servicing asset - ending balance	9,120
Residential loan
Servicing Asset at Amortized Cost [Line Items]
Proceeds from sale of mortgage loans	72,500	24,900
Gain on sale of mortgage loans	2,000	600
Servicing contracts
Servicing Asset at Amortized Cost [Line Items]
Gross carrying amount			22,178	$ 21,543
Accumulated amortization			13,058	(12,442)
Valuation allowance	0	0	0	0	0
Net carrying amount			9,120	9,101	$ 7,897
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Servicing asset - beginning balance	9,101	8,062
Amount capitalized	636	230
Amortization	(617)	(395)
Other-than-temporary impairment	0	0
Servicing asset - ending balance	9,120	7,897
Valuation Allowance [Roll Forward]
Valuation allowance, beginning balance	0	0
Provision (recovery)	0	0
Other-than-temporary impairment	0	0
Valuation allowance, ending balance	$ 0	$ 0
Unpaid principal balance			1,308,847	1,276,437
Prepayment rate:
25 basis points adverse rate change			(1,052)	(950)
50 basis points adverse rate change			(1,921)	(1,947)
Discount rate:
25 basis points adverse rate change			(71)	(102)
50 basis points adverse rate change			$ (140)	$ (202)
Servicing contracts | Note rate
Valuation Allowance [Roll Forward]
Weighted average measurement input			0.0394	0.0396
Servicing contracts | Discount rate
Valuation Allowance [Roll Forward]
Weighted average measurement input			0.093	0.093
Servicing contracts | Prepayment speed
Valuation Allowance [Roll Forward]
Weighted average measurement input			0.167	0.114