Derivative instruments (Amount included in statement of operations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Not designated as hedging instruments | Foreign exchange gain (loss)
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ (1,667)	$ (610)	$ 0
Not designated as hedging instruments | Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net	142	139	(133)
Not designated as hedging instruments | Gain (Loss) on Investments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net	8,518	0	0
Designated as hedging instruments | Fair value hedge | Foreign currency forward contracts | Foreign exchange gain (loss)
Derivatives designated as fair value hedges and related hedged item
Amount of gain (loss) recognized in income on derivative	0	(12,279)	(9,651)
Amount of gain (loss) on hedged item recognized in income attributable to risk being hedged	0	12,279	9,651
Amount of gain (loss) recognized in income on derivative (ineffective portion)	0		0
Designated as hedging instruments | Cash flow hedge | Interest rate swap contracts
Derivative Instruments designated as a cash flow hedge
Amount of ineffective portion excluded from effectiveness testing	277	(841)	(228)
Designated as hedging instruments | Cash flow hedge | Interest rate swap contracts | Other comprehensive income
Derivative Instruments designated as a cash flow hedge
Amount of effective portion recognized in other comprehensive income	10,584	13,740	13,302
Designated as hedging instruments | Cash flow hedge | Interest rate swap contracts | Finance expenses
Derivative Instruments designated as a cash flow hedge
Amount of effective portion subsequently reclassified to earnings	$ (10,861)	$ (12,899)	$ (13,074)