Financial Instruments Realized and unrealized gains (losses) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Derivative [Line Items]
Realized and unrealized gain (loss) on derivatives	$ 272	$ (911)	$ 441	$ 1,561
Cross-currency option
Derivative [Line Items]
Realized and unrealized gain (loss) on derivatives	0	(84)	0	(84)
Foreign currency forward contracts
Derivative [Line Items]
Realized and unrealized gain (loss) on derivatives	$ 272	$ (827)	$ 441	$ 1,645