Income taxes (Movement in tax carryforwards and valuation allowance) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Tax Credit Carryforward [Line Items]
Balance at beginning of year	$ 167,929
Balance at beginning of year	(167,929)
Balance at end of year	116,416
Balance at end of year	(98,065)
Deferred Tax Asset on Tax Losses Carried Forward
Tax Credit Carryforward [Line Items]
Balance at beginning of year	167,929
Movement due to use of tax losses carried forward	(10,990)
Movement due to provision to return adjustments	1,108
Movement due to changes in enacted tax rates	(8,757)
Movement due to change in assessment of deferred tax asset recoverability	0
Forfeiture of tax losses carried forward	(32,927)
Other	53
Balance at end of year	116,416
Valuation Allowance
Tax Credit Carryforward [Line Items]
Balance at beginning of year	(167,929)
Movement due to use of tax losses carried forward	10,990
Movement due to provision to return adjustments	(1,108)
Movement due to changes in enacted tax rates	8,757
Movement due to change in assessment of deferred tax asset recoverability	18,351
Forfeiture of tax losses carried forward	32,927
Other	(53)
Balance at end of year	(98,065)
Luxembourg | Deferred Tax Asset on Tax Losses Carried Forward
Tax Credit Carryforward [Line Items]
Movement due to use of tax losses carried forward	6,722
Movement due to changes in enacted tax rates	(8,757)
Forfeiture of tax losses carried forward	18,438
Luxembourg | Valuation Allowance
Tax Credit Carryforward [Line Items]
Movement due to change in assessment of deferred tax asset recoverability	18,351
United States | Deferred Tax Asset on Tax Losses Carried Forward
Tax Credit Carryforward [Line Items]
Movement due to use of tax losses carried forward	3,066
Singapore | Deferred Tax Asset on Tax Losses Carried Forward
Tax Credit Carryforward [Line Items]
Movement due to use of tax losses carried forward	1,202
Switzerland | Deferred Tax Asset on Tax Losses Carried Forward
Tax Credit Carryforward [Line Items]
Forfeiture of tax losses carried forward	$ 14,489