Pensions - Components of Net Periodic Pension Costs and Cash Contributions (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Contributions to pension plans
Employer contributions made			$ 2,104	$ 1,646
United States
Components of net periodic pension costs of the plans
Service cost	$ 239	$ 239	719	717
Interest cost	1,103	1,146	3,309	3,443
Expected return on plan assets	(1,443)	(1,512)	(4,390)	(4,529)
Net actuarial loss amortization	746	753	2,240	2,257
Settlement		76		756
Net periodic pension cost	645	702	1,878	2,644
Contributions to pension plans
Employer contributions made			800
European
Components of net periodic pension costs of the plans
Service cost	135	93	383	279
Interest cost	246	280	714	877
Expected return on plan assets	(334)	(348)	(973)	(1,100)
Amortization of prior service credit	(3)		(7)
Net actuarial loss amortization	115	57	332	174
Net periodic pension cost	$ 159	$ 82	$ 449	$ 230