Income taxes (Loss carryforwards) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	$ 486,462
Gross deferred tax asset	115,579	$ 116,416
Valuation allowance	(86,272)	$ (98,065)
Net deferred tax asset	29,307
Estimated accrual of withholding tax	878
Luxembourg
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	276,819
Gross deferred tax asset	72,001
Valuation allowance	(53,899)
Net deferred tax asset	18,102
Switzerland
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	145,669
Gross deferred tax asset	30,590
Valuation allowance	(27,347)
Net deferred tax asset	3,243
United States
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	52,108
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	5,755
Gross deferred tax asset	10,943
Valuation allowance	(4,794)
Net deferred tax asset	$ 6,149
Loss carryback period	2 years
Loss carryforward period	20 years
United Kingdom
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	$ 9,543
Gross deferred tax asset	1,813
Valuation allowance	0
Net deferred tax asset	1,813
Singapore
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	2,323
Gross deferred tax asset	232
Valuation allowance	(232)
Net deferred tax asset	0
Expiring 2018-2020
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	145,669
Expiring 2018-2020 | Luxembourg
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	0
Expiring 2018-2020 | Switzerland
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	145,669
Expiring 2018-2020 | United States
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	0
Expiring 2018-2020 | United Kingdom
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	0
Expiring 2018-2020 | Singapore
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	0
Expiring 2029-2038
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	22,827
Expiring 2029-2038 | Luxembourg
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	0
Expiring 2029-2038 | Switzerland
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	0
Expiring 2029-2038 | United States
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	22,827
Expiring 2029-2038 | United Kingdom
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	0
Expiring 2029-2038 | Singapore
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	0
No Expiration Date
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	317,966
No Expiration Date | Luxembourg
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	276,819
No Expiration Date | Switzerland
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	0
No Expiration Date | United States
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	29,281
No Expiration Date | United Kingdom
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	9,543
No Expiration Date | Singapore
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	2,323
Insurance Segment | No Expiration Date | United States
Operating and Capital Loss Carryforwards [Line Items]
Loss Carryforwards	$ 7,768