Bank segment - Mortgage servicing rights (Details) - American Savings Bank (ASB) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)
Servicing Asset at Amortized Cost [Line Items]
Repurchase reserve					$ 100		$ 100
Mortgage service fees	$ 800	$ 700	$ 1,500	$ 1,500
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	8,509		8,509
Residential loan
Servicing Asset at Amortized Cost [Line Items]
Proceeds from sale of mortgage loans	44,300	39,300	77,400	79,900
Gain on sale of mortgage loans	600	600	1,200	1,400
Servicing contracts
Servicing Asset at Amortized Cost [Line Items]
Gross carrying amount					18,238	$ 17,511
Accumulated amortization					(9,729)	(8,872)
Valuation allowance	0	0	0	0	0	0	0
Net carrying amount					8,509	8,639	$ 9,181
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Servicing asset - beginning balance	8,541	9,294	8,639	9,373
Amount capitalized	392	362	727	798
Amortization	(424)	(475)	(857)	(990)
Other-than-temporary impairment	0	0	0	0
Servicing asset - ending balance	8,509	9,181	8,509	9,181
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					1,192,901	1,195,454
Prepayment rate:
25 basis points adverse rate change					(344)	(869)
50 basis points adverse rate change					(797)	(1,828)
Discount rate:
25 basis points adverse rate change					(135)	(111)
50 basis points adverse rate change					$ (268)	$ (220)
Servicing contracts | Note rate
Valuation Allowance [Roll Forward]
Weighted average measurement input					0.0396	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					0.068	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%