Bank segment - Mortgage servicing rights (Details) - American Savings Bank (ASB) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)
Servicing Asset at Amortized Cost [Line Items]
Repurchase reserve					$ 100		$ 100
Mortgage service fees	$ 900	$ 800	$ 2,500	$ 2,200
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	9,553		9,553
Residential loan
Servicing Asset at Amortized Cost [Line Items]
Proceeds from sale of mortgage loans	128,000	87,800	387,200	177,300
Gain on sale of mortgage loans	7,700	1,500	15,900	3,100
Servicing contracts
Servicing Asset at Amortized Cost [Line Items]
Gross carrying amount					25,024	$ 21,543
Accumulated amortization					(15,089)	(12,442)
Valuation allowance	(382)	0	(382)	0	(382)	0	0
Net carrying amount					9,553	9,101	$ 8,567
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Servicing asset - beginning balance	9,911	8,103	9,101	8,062
Amount capitalized	1,119	995	3,481	1,857
Amortization	(1,095)	(531)	(2,647)	(1,352)
Other-than-temporary impairment	0	0	0	0
Servicing asset - ending balance	9,935	8,567	9,935	8,567
Valuation Allowance [Roll Forward]
Valuation allowance, beginning balance	264	0	0	0
Provision (recovery)	118	0	382	0
Other-than-temporary impairment	0	0	0	0
Valuation allowance, ending balance	$ 382	$ 0	$ 382	$ 0
Unpaid principal balance					1,456,434	1,276,437
Prepayment rate:
25 basis points adverse rate change					(826)	(950)
50 basis points adverse rate change					(1,524)	(1,947)
Discount rate:
25 basis points adverse rate change					(65)	(102)
50 basis points adverse rate change					$ (129)	$ (202)
Servicing contracts | Note rate
Valuation Allowance [Roll Forward]
Weighted average measurement input					0.0377	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					0.178	0.114