Bank segment - Mortgage servicing rights (Details) - American Savings Bank (ASB) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)
Servicing Asset at Amortized Cost [Line Items]
Repurchase reserve					$ 100		$ 100
Mortgage service fees	$ 800	$ 800	$ 1,600	$ 1,500
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	9,647		9,647
Residential loan
Servicing Asset at Amortized Cost [Line Items]
Proceeds from sale of mortgage loans	186,800	64,700	259,300	89,600
Gain on sale of mortgage loans	6,300	1,000	8,300	1,600
Servicing contracts
Servicing Asset at Amortized Cost [Line Items]
Gross carrying amount					23,904	$ 21,543
Accumulated amortization					(13,993)	(12,442)
Valuation allowance	0	0	0	0	(264)	0	0
Net carrying amount					9,647	9,101	$ 8,103
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Servicing asset - beginning balance	9,120	7,897	9,101	8,062
Amount capitalized	1,726	632	2,362	862
Amortization	(935)	(426)	(1,552)	(821)
Other-than-temporary impairment	0	0	0	0
Servicing asset - ending balance	9,911	8,103	9,911	8,103
Valuation Allowance [Roll Forward]
Valuation allowance, beginning balance	0	0	0	0
Provision (recovery)	264	0	264	0
Other-than-temporary impairment	0	0	0	0
Valuation allowance, ending balance	$ 264	$ 0	$ 264	$ 0
Unpaid principal balance					1,360,920	1,276,437
Prepayment rate:
25 basis points adverse rate change					(539)	(950)
50 basis points adverse rate change					(1,062)	(1,947)
Discount rate:
25 basis points adverse rate change					(64)	(102)
50 basis points adverse rate change					$ (128)	$ (202)
Servicing contracts | Note rate
Valuation Allowance [Roll Forward]
Weighted average measurement input					0.0387	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					0.169	0.114