Pensions - Components of Net Periodic Pension Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
U.S. Plans
Components of net periodic pension costs of the plans
Service cost	$ 239	$ 285	$ 717	$ 853
Interest cost	1,146	1,138	3,443	3,365
Expected return on plan assets	(1,512)	(1,783)	(4,529)	(5,349)
Amortization of prior service cost		4		11
Net actuarial loss amortization	753	646	2,257	1,916
Settlement	76	480	756	480
Net periodic pension cost (benefit)	702	770	2,644	1,276
European Plans
Components of net periodic pension costs of the plans
Service cost	93	72	279	217
Interest cost	280	309	877	920
Expected return on plan assets	(348)	(421)	(1,100)	(1,251)
Net actuarial loss amortization	57	54	174	163
Net periodic pension cost (benefit)	$ 82	$ 14	$ 230	$ 49