Other expense, net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Income and Expenses [Abstract]
Currency transaction (gains)/losses	$ (3,611)	$ 261	$ (2,930)	$ 2,310
Bank fees	100	116	303	375
Gain on insurance recovery		(2,000)		(2,000)
Components of net periodic pension and postretirement cost other than service	282	625	807	1,874
Other	78	468	847	295
Total	$ (3,151)	$ (530)	$ (973)	$ 2,854