Other expense, net (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other Income and Expenses [Abstract]
Currency transaction (gains)/losses	$ (9)	$ 1,948	$ 681	$ 2,049
Bank fees	96	111	204	259
Components of net periodic pension and postretirement cost other than service	259	627	525	1,249
Other	380	(128)	768	(173)
Total	$ 726	$ 2,558	$ 2,178	$ 3,384