Financial Instruments Realized and unrealized gains (losses) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Derivative [Line Items]
Realized and unrealized gain (loss) on derivatives	$ 511	$ (313)	$ 952	$ 1,247
Cross-currency option
Derivative [Line Items]
Realized and unrealized gain (loss) on derivatives	0	27	0	(57)
Foreign currency forward contracts
Derivative [Line Items]
Realized and unrealized gain (loss) on derivatives	$ 511	$ (340)	$ 952	$ 1,304